Diamonds - gemstonebookstore

Diamonds
W. Dan Hausel
INTRODUCTION
quenching. Lonsdaleite has since been identified in meteorites and
in rare unconventional host rocks, the most notable being the Popigay Depression in Siberia (Erlich and Hausel 2002). The extreme
hardness of lonsdaleite makes it ideal for industrial grinding, but its
rarity makes it unattractive for commercial use.
Diamond is an extraordinary mineral with extreme hardness and
inherent beauty that is sought for personal adornment and industrial
use. Because the genesis of this unique mineral requires extreme
temperature and pressure, natural diamond is rare—so rare that
some diamonds are the most valuable commodity on earth, based
on weight.
Diamonds are mined on several continents. The value of the
raw production has resulted in a multi-billion-dollar industry.
Natural diamond production annually averages more than 110 million carats, valued at more than $7 billion for the raw stones. Diamond values dramatically increase following the fashioning of the
stones, and the value again dramatically increases with their dressing in jewelry, such that diamond jewelry typically sells for 10 to
100 times the value of the raw stone. Industrial diamonds, which
are of considerably lower value, include synthetic industrial diamonds. Synthetic industrial diamond production has an average
annual value of about $1 billion.
Crystal Habit
Diamonds are isometric with cubic, octahedral, hexoctohedral,
dodecahedral, trisoctahedral, and related habits. Twinning along the
octahedral {111} plane is common, and many crystals are often
flattened parallel to this plane, producing a habit that appears as
flattened, triangular-shaped diamond known as a macle.
Cube
Cubes are a relatively uncommon habit for diamond, and when
found are primarily frosted industrial stones. Many have been found
in placers in Brazil, and a significant percentage of diamonds in the
Snap Lake kimberlites of Canada have cubic habit (Pokhilenko et al.
2003). Crystal faces of a cube often exhibit square-shaped pyramidal
depressions rotated 45° diagonally to the edge of the crystal face.
The cube may also include scattered trigons mixed with pyramidal
and other depressions of hexagonal morphology visible with a
microscope.
MINERALOGY
Diamond consists simply of carbon. In nature, native carbon may
occur as one of the following polymorphs: diamond, graphite, or
lonsdaleite (Erlich and Hausel 2002). The physical differences
among these polymorphs reflect the different bonds between the
carbon atoms in the crystal structure. In diamond, the coordination
of the carbon atoms is tetrahedral with each atom held to four
others by strong covalent bonds, resulting in a mineral with extreme
hardness.
In contrast, graphite has six-member hexagonal carbon rings
that resonate between single- and double-shared electron bonds.
These graphite sheets are very strong, but the hexagonal rings are
stacked and do not share electrons between adjacent sheets, only a
residual electrical charge—thus, no chemical bonds occur between
the sheets, resulting in graphite being soft and the sheets easily
separated.
The hexagonal modification of diamond, known as lonsdaleite, has a closer-packed arrangement of atoms than diamond or
graphite, resulting in a rare mineral of extreme hardness (Lonsdale
1971). Lonsdaleite was initially synthesized at temperatures greater
than 1,000°C (1,830° F) under static pressures exceeding 130 kbar
(Bundy and Kasper 1967). DuPont deNemours and Co. obtained
the same transformation by intense shock compression and thermal
Octahedron
The octahedron is an eight-sided crystal that has the appearance of 2
four-sided pyramids attached at a common base. Each pyramid contains four equilateral triangles known as octahedral faces. In nature,
an octahedral face will often have positive or negative trigons—small
equilateral triangles that are visible under a microscope. These are
growths or etches on the crystal surface that represent disequilibrium during transport to the earth’s surface from the initial stable
conditions at depth within the mantle.
Partial resorption of the octahedron will result in different
crystal habits, including a rounded dodecahedron (12-sided) with
rhombic faces. Further resorption may result in ridges on the rhombic faces, yielding a 24-sided crystal known as a trishexahedron.
Many diamonds from Argyle, Australia; Murfreesburo, Arkansas;
and the Colorado–Wyoming State Line District exhibit resorbed
crystal habits. Four-sided tetrahedral diamonds are sometimes
encountered that are distorted octahedrons (Orlov 1977; Bruton
1979).
1
2
Industrial Minerals and Rocks
Diamonds commonly enclose mineral inclusions along cleavage planes. These tiny inclusions provide important data on the origin of diamond and can be used to determine the age of the stone
or to identify the unique chemistry associated with the genesis of
diamond.
Bort
Bort is poor-grade diamond used as an industrial abrasive. It forms
rounded grains with a rough exterior and has a radiating crystal
habit. The term is also applied to diamonds of inferior quality and
to small diamond fragments.
Carbonado
Carbonado is a black to grayish, opaque, fine-grained aggregate of
microscopic diamond, graphite, and amorphous carbon with or without accessory minerals. The material is hard, occurs mainly as irregular porous concretions and dendritic aggregates of minute octahedra,
and sometimes forms regular, globular concretions. Carbonado is
characterized by large aggregates (averaging 8 to 12 mm in diameter)
that commonly weigh as much as 20 carats. Specimens of several
hundred carats are not uncommon. The density for carbonado is less
than that for diamond and varies from 3.13 to 3.46 gm/cm3.
Although carbonado had been found in placers in Brazil and
Russia, it was not until the 1990s that it was found in situ. Twentysix grains of carbonado ranging in size from 0.1 to 1 mm were
recovered from a 330-lb sample taken from avachite (a specific type
of basalt from the Avacha volcano of eastern Kamchatka) (Smishlyaev 1999; Erlich and Hausel 2002).
Physical Properties of Diamond
Diamond exhibits perfect octahedral cleavage with conchoidal fracture. The mineral is brittle and will easily break with a mild strike
of a hammer. Even so, it is the hardest of all naturally occurring
minerals and is assigned a hardness of 10 on the Mohs scale and
nearly 8,000 kg/mm2 on the Knoop scale. Corundum, the next hardest naturally occurring mineral, has a Mohs hardness of 9. Even so,
corundum does not even compare to diamond and only has a Knoop
scale hardness of 1,370 kg/mm2. Because of diamond’s extreme
hardness and excellent transparency, diamond is extensively used in
jewelry and has a variety of industrial uses.
Diamond’s hardness varies in different crystallographic directions. This allows for the mineral to be polished with less difficulty
in specific directions using diamond powder. For example, it is less
difficult to grind the octahedral corners off the diamond, whereas
grinding parallel to the octahedral face is nearly impossible.
With perfect cleavage in four directions parallel to the octahedral faces, an octahedron can be fashioned from an irregular
diamond by cleaving (Orlov 1977). The specific gravity of diamond (3.516 to 3.525) is high enough that the gem will concentrate in placers with “black sand.” This density is surprisingly
high, given that it is composed of such a light element. Compared
to graphite, diamond is twice as dense because of the close packing of atoms.
Color
Diamonds occur in a variety of colors, including white to colorless
and shades of yellow, red, pink, orange, green, blue, brown, gray,
and black. Those that are strongly colored are termed fancies. Colored diamonds have included some spectacular stones. For example,
at the 1989 Christie’s Auction in New York, a 3.14-carat Argyle
pink sold for $1.5 million. More recently, a 0.95-carat fancy purplish
red Argyle diamond sold for nearly $1 million. The world’s largest
faceted diamond, a yellow-brown fancy known as the 545.7-carat
Golden Jubilee (Harlow 1998), is considered priceless. Possibly the
most famous diamond in the world, the 45-carat Hope, is a blue
fancy.
In most other gemstones, color is the result of minor transition
element impurities; however, this is not the case for diamond. Color
in many diamonds is related to nitrogen and boron impurities or is
the result of structural defects. Diamonds with dispersed nitrogen
may produce yellow (canary) gemstones. If the diamond contains
some boron, it may be blue, such as the Hope diamond. The Hope
was found in India; however, many natural blue diamonds have
come from the Premier mine in South Africa. Blue diamonds with
traces of boron are referred to as type IIb diamonds and are semiconductors. Natural irradiation may also result in blue coloration in
some diamonds (Harlow 1998).
The most common color for diamond is brown. Before the
development of the Argyle mine in Australia in 1986, brown diamonds were considered industrial stones. But because of Australian
marketing strategies, brown diamonds are now highly prized gems.
The lighter brown stones are labeled champagne and the darker
brown referred to as cognac. Yellow is the second most common
color, and such stones are referred to as Cape diamonds in reference
to the Cape Province of South Africa. When the yellow color is
intense, the stone is referred to as canary.
Pink, red, and purple diamonds are rare. The color in these is
concentrated in tiny lamellae (referred to as pink graining) in an
otherwise colorless diamond. The color lamellae are thought to be
the result of deformation of the diamond structure.
Even though there are many green diamonds, few are faceted, primarily because most have a thin green surface layer covering clear diamond that is removed during faceting. Faceted
green diamonds are so rare that only one is relatively well known
(the 41-carat Dresden Green), and is thought to have either originated in India or Brazil. The color in most green diamonds is the
result of natural irradiation. Other green diamonds may result
from hydrogen impurities. Another variety, known as a green
transmitter, produces strong fluorescence that tends to mask the
yellow color of the stone. Other colors include rare orange and
violet diamonds (Harlow 1998).
One of the better-known black diamonds is the 67.5-carat
Orlov. Black diamonds are colored by numerous graphite inclusions, which also make the diamond an electrical conductor. These
are difficult to polish because of abundant soft graphite, so black
gem diamonds are uncommon. Opalescent, or fancy milky white
diamond is the result of numerous mineral inclusions and possibly
nitrogen defects in the crystal (Harlow 1998).
Dispersion, Transparency, Conductivity, Wet Ability
Diamond has a high coefficient of dispersion (0.044), the coefficient is the difference in refractive index of two visible light
wavelengths at the opposite ends of the spectrum (one blue-violet
and the other red), resulting in the distinct fire seen in faceted diamond caused by its high dispersion. Diamond is completely transparent to a broad segment of the electromagnetic spectrum,
making it useful in a variety of industrial, electrical, and scientific
applications. It is also transparent to radio and microwaves. Colorless diamonds are also transparent to visible light wavelengths
extending into the ultraviolet (UV), and a few rare diamonds (type
II) are transparent over much of the UV spectrum (Harlow 1998).
Diamond has a luster described as greasy to adamantine that is
related to its high refractive index (IR = 2.4195) and density. Such
high density greatly diminishes the speed of light. For example, the
speed of light in a vacuum is 186,000 miles/sec (300,000 km/sec),
but in diamond, it is only 77,000 miles/sec (Harlow 1998).
Diamonds
Somerset
Island
AV
E
RAE
Lac de Gras
NAIN
SL
HEARNE
Sturgeon
Lake
Archon
nv
ill
Kirkland
Lake
re
SUPERIOR
Fort a la Corne
Noranda
Lake
Ellen
WYOMING
EXPLANATION
n
e
ego
G
Or
Trans-Hudson
Many diamonds are luminescent: approximately one third of
all diamonds luminesce blue when placed in UV light. In most
cases, luminescence will stop when the UV light is turned off
(known as fluorescence). Diamonds fluoresce in both long- and
short-wave UV light. The fluorescence is usually greater in longwave light, and diamond may appear blue, green, yellow, or occasionally red. Fluorescence is generally weak, however, and it may
not be readily apparent to the naked eye. In some cases, light emission is still visible for a brief interval after the UV light source is
turned off (known as phosphorescence). Some diamonds may also
show brilliant phosphorescence when rubbed or exposed to the
electric charge in a vacuum tube, or when exposed to UV light
(Dana and Ford 1951).
At room temperature, diamond is four times as thermally conductive as copper, even though it is not electrically conductive.
Because of the ability to conduct heat, diamond has a tendency to
feel cool to the lips when touched, since the gemstone conducts
heat away from the lips. This is why diamonds have been referred
to as ice. Gem testers (about the size of a pen) are designed to identify the unique thermal conductivity of diamond and distinguish it
from other gems and imitations.
Diamonds are hydrophobic (nonwettable). Even though diamond is 3.5 times heavier than water, it can be induced to float on
water. Because it is hydrophobic, diamond will attract grease, thus
providing an efficient method for extracting diamond from ore
concentrates (i.e., grease table).
Diamonds are unaffected by heat except at high temperatures.
When heated in oxygen, diamond will burn to carbon dioxide
(CO2). Without oxygen, diamond will transform to graphite at
much higher temperatures (1,900°C [3,450°F]). Diamonds are
unaffected by acids.
3
State Line
district
Prairie Creek
Proton
Tecton
Diamond-bearing
occurrences
0
500
1,000 km
Adapted from Levinson, Gurney, and Kirkley 1992.
Figure 1. The North American craton showing regions of
favorability for conventional diamondiferous host rocks. Major
Archean provinces are in all capital letters.
ORIGIN AND OCCURRENCE
There are literally thousands of known kimberlites and many hundreds of lamproites and lamprophyres, but only a handful contain
commercial amounts of diamond. One estimate made many years
ago suggested that less than 1% of all kimberlites are commercially mineralized (Lampietti and Sutherland 1978). Although
many hundreds of new discoveries have been made since that
paper was published, this statistic remains essentially valid.
Diamondiferous kimberlites and lamproites are essentially
restricted to cratons and cratonized terrains. These include stable
Archean cratonic cores (known as Archons) as well as cratonized
Proterozoic margins (referred to as Protons) (Figure 1). Some
unconventional diamondiferous host rocks have also been identified
in cratons and outside cratonic terrains within tectonically active
regions along the margins of cratons. Because high ore grades have
been detected in some of these, unconventional commercial host
rocks are anticipated to be found in the future (Erlich and Hausel
2002). Current diamond exploration programs are designed to
search for conventional host rocks (i.e., kimberlite and lamproite)
or for placers presumably derived from these.
Most diamonds are considered xenocrysts that separated from
disaggregated mantle peridotite and eclogite during transportation to
the earth’s surface in kimberlitic, lamproitic, and some lamprophyric
magmas. Kimberlites, lamproites, and lamprophyres tend to occur in
clusters of a few to more than 100 occurrences. Structural control is
thought to be important in the emplacement of these, and several
structural orientations are often recognized within each district.
Kimberlite
The majority of diamond mines are developed in kimberlite such as
the Wesselton, DeBeers, Kimberley, Dutoitspan, and Ekati, or in
placers, particularly beach placers along the west coast of Africa.
Lampietti and Sutherland (1978) reported that only about 10% of
the known kimberlites were mineralized with diamond. This statistic may no longer be valid in that as many as 50% of kimberlites
found in Canada and Wyoming in recent years, and possibly as
many as 90% in Colorado, have yielded diamond. Even so, only a
very small portion is commercially mineralized. When economic,
kimberlites may contain hundreds of millions to billions of dollars
worth of stones; thus kimberlite should be a priority target in any
exploration program.
Kimberlites are essentially carbonated alkali peridotites that
exsolve CO2 during ascent to the surface from the earth’s upper
mantle, resulting in diatremes with considerable brecciation and
dissolution-rounded xenoliths and cognate nodules. The diatremes
appear as subvertical to vertical pipes that taper down at depth,
forming steeply inclined cylindrical bodies. The average angle of
inclination of the walls of various pipes in the Kimberley region of
South Africa (Wesselton, DeBeers, Kimberley, and Dutoitspan) is
82° to 85°. Ideally, the pipes have rounded to ellipsoidal horizontal
cross-sections filled with kimberlitic tuff or tuff-breccia. Many continue from the surface to depths of 2 to 2.4 km, where they pinch
down to narrow root zones emanating from a feeder dike.
The Kimberley pipe, which was mined out by 1915 (about
20 years after discovery), contracted sharply at depth. At the lowest level of mining (1,056 m), it was no longer pipe shaped but
rather had the appearance of three intersecting dikes (Kennedy
and Nordlie 1968). Combined with the estimated 1,600 m of erosion since the time of emplacement, the depth to the original point
of expansion was probably 2.4 km.
4
Industrial Minerals and Rocks
Courtesy of W.D. Hausel.
Figure 2. Exposed contact of a Schaffer diamondiferous kimberlite,
Wyoming, showing the knife sharp contact between the kimberlite
(left) and granite (right), explained by adiabatic cooling of the
kimberlite magma during eruption
Kimberlitic magmas are interpreted to originate from depths
as great as 200 km and travel to the earth’s surface in a matter of
hours (O’Hara, Richardson, and Wilson 1971). The magma is
thought to rise rapidly, possibly 10 to 30 km/hr in order to transport
high-density ultramafic xenoliths. Within the last few kilometers of
the surface, emplacement rates are thought to increase dramatically
to several hundred kilometers per hour. Such velocities could bring
diamonds from the mantle to the surface in less than a day.
McGretchin (1968) estimated that the speed of the fluidized material near the surface increased to as much as 400 m/sec, or about the
speed of sound (Mach 1 or 331 m/sec). Some estimates have even
suggested kimberlite emplacement at the earth’s surface may have
achieved velocities exceeding Mach 3 (Hughes 1982).
The temperature of the magma at the point of eruption is relatively cool (Figure 2). Watson (1967) indicated a magma temperature of less than 600°C (1,110°F) on the basis of the coking effects
on coal intruded by kimberlite. A low temperature of emplacement
is also supported by the absence of any visible thermal effects on
country rock adjacent to most kimberlite contacts. Davidson (1967)
suggested the temperature of emplacement may have been as low as
200°C based on the retention of argon. Hughes (1982) pointed out
that the near-surface temperatures of the gas-charged kimberlite
melt may be as low as 0°C (32°F) because of the adiabatic expansion of CO2 gas as kimberlite erupts at the surface.
Kimberlites typically transport xenoliths and xenocrysts to the
surface. Many of these are derived from mantle depths and some
form a distinct suite of minerals that are referred to as kimberlitic
indicator minerals. The traditional indicator minerals used to
explore for kimberlite include pyrope garnet, chromian diopside,
chromian enstatite, picroilmenite, chromite, and diamond.
Lamproite
Serious interest in lamproite intensified following the discovery of
a world-class diamond deposit in olivine lamproite in 1979 in the
Kimberley region at Argyle, Western Australia. The discovery led
to the recognition of other diamondiferous lamproites in Australia,
Brazil, China, Gabon, Zambia, Ivory Coast, India, Russia, and the
United States.
Scott-Smith (1996) subdivides lamproites into two general
groups: phlogopite-leucite lamproites (~60% SiO2 [silicon dioxide])
and olivine lamproites (>20% MgO [magnesium oxide], 35% to
45% SiO2, and 7% K2O [potassium oxide]) with abundant serpentine pseudomorphs after olivine. Instead of pipes with steep walls
that slowly diminish in diameter with increasing depth, lamproites
are characterized by “champagne-glass” vents filled by tuffaceous
rocks, often with massive volcanic rocks in the core.
In some cases, lamproites appear to have formed in the diamond stability field (Nixon 1995). A qualitative correlation
between diamond and olivine in lamproite is confirmed in both the
Ellendale, Australia, and Kapamba, Zambia, provinces in which
diamond grades are consistently higher in olivine lamproites than
leucite lamproites. When found, diamonds occur primarily in pyroclastic rocks; the magmatic phases are notoriously diamond poor,
owing to the high temperatures sustained in the flows during eruption, which are antipathetic to diamond preservation; that is, the
diamonds will burn (Scott-Smith 1986).
Where vents flare out, a potential for substantial tonnages
exists in larger craters. At Argyle, Western Australia, past reserve
estimates of 94 Mt of ore at an average grade of 750 carats/100 t led
to its classification as a world-class deposit. Some of the richer portions of this deposit yielded grades as high as 2,000 carats/100 t.
Large numbers of the Argyle diamonds, however, are graphitized
and partially resorbed; more than 60% are irregular in shape and
include macles, polycrystalline forms, and rounded dodecahedrons.
The largest Argyle diamond weighed 42.6 carats; the overall size of
diamonds is quite small (average <0.1 carat). Nearly 80% are
brown, and the remaining stones are dominantly yellow or colorless. Rare but economically important pink to red diamonds bring
Argyle fame (Shigley, Chapman, and Ellison 2001).
Many lamproitic diamonds are relatively small and include
common fancy yellow to brown stones. For example, macro diamonds (>1 mm) from the Ellendale field in Western Australia are
dominantly yellow dodecahedra, and many micro diamonds are
colorless or pale-brown, frosted, step-layered octahedral (Shigley,
Chapman, and Ellison 2001).
Placers
Because of a relatively high specific gravity (3.5) and extreme hardness, diamonds are often found in secondary stream or marine placers with other minerals of relatively high specific gravity such as
magnetite, spinel, ilmenite, rutile, garnet, and gold. Some of the
more productive deposits include stream and marine placers where
a large percentage of diamonds are gem quality, owing to fracturing
and disaggregation of imperfect industrial diamonds during stream
transport. Considerable numbers of diamonds have been mined
from stream sediments along the Orange River basin in southern
Africa and continuing in beach sands downcurrent from the mouth
of the Orange River along the Atlantic coast. Historically, there
have been many reports of gold prospectors finding diamonds while
searching for placer gold. Examples include California, Colorado,
Georgia, North Carolina, and Wyoming in the United States, and
New South Wales in Australia (Hausel 1998).
Placer diamond deposits formed throughout geological history as is evident by diamonds in ancient Proterozoic paleoplacers
in the Witwatersrand metaconglomerates of South Africa and the
Snowy Range Group in Wyoming, United States, as well as modern
placers along the Atlantic coast of Africa and Smoke Creek near the
Argyle mine, Australia.
Diamonds
DISTRIBUTION AND PRODUCTION
Diamond Production
Diamonds are mined from at least 20 countries, and the leading producers of natural diamond are Australia, Botswana, Canada, South
Africa, Russia, and Zaire. The World Diamond Council estimated
that natural diamond production in 1999 was more than 111 million
carats, valued at US$7.4 billion. In 2000, diamond production was
estimated at more than 110 million carats, valued at US$7.9 billion.
In 2001, the U.S. Geological Survey (USGS) estimated that 119 million carats were mined, with an estimated value of US$7.3 billion,
and in 2003, diamond production estimates stood at 132 million carats (Olson 2003). The Northern Miner (Anon. 2005) reported that
rough diamond sales in 2003 for the Diamond Trading Company
(DeBeers marketing arm) were $5.52 billion.
Canada ranked sixth in diamond production during the same
period, but in the second quarter of 2004, it surpassed South Africa
to become the third largest diamond producer (based on value).
This is one of the great exploration success stories of the twentieth
century because before 1998, Canada did not have a diamond
industry (Krajick 2001).
Industrial diamonds have considerably less value than gem diamond, and much of industrial production is now synthetic. In 2001,
nearly 70% of the total natural and synthetic industrial diamond production came from Ireland, Russia, and the United States: 92% was
synthetic (Olson 2001). According to the USGS, world production of
natural industrial diamond totaled 48 million carats in 2001 and 48.9
million carats in 2002. More than one third of the world’s natural diamond production was classified as industrial. This represented only a
very small percentage (~1%), however, of the total monetary value of
natural diamond production. Australia led the market in recovery of
natural industrial diamonds and has averaged 22.1 million carats per
year; however, declining reserves at the Argyle mine resulted in Australian industrial diamond production of only 13.1 million carats in
2001 and in 2002 (Olson 2003).
The World Diamond Council reported that the United States
was the largest producer of synthetic industrial diamonds, with 125
million carats manufactured in 1999. The USGS reported that
domestic synthetic industrial diamond production for 2002 was
310 million carats. The total industrial output worldwide was estimated to be in excess of 800 million carats in 2001, valued at more
than US$600 million (Olson 2001). Domestic synthetic diamonds
were produced by two companies: GE Superabrasives in Ohio and
Mypodiamond Inc. in New Jersey.
Natural diamond production was dominated by southern African countries with a significant contribution by Russia and Australia. Nearly all of the Australian diamond production was from the
Argyle mine, which accounted for more than 20% of world’s diamonds. The relatively low quality of the Argyle diamonds, however, rendered the production to be less valuable than some smaller
operations elsewhere.
Diamond Distribution
Although there are hundreds of known diamond occurrences around
the world, commercial diamond deposits are rare. In the richest, diamond occurs in concentrations of much less than 1 ppm (Lampietti
and Sutherland 1978). The few commercial diamond deposits are
hosted by kimberlite, lamproite, and placers derived from these host
rocks. These are all associated with Archean cratons and cratonized
Proterozoic belts. The discovery of several unconventional host rocks
in recent years, though, some with very high ore grades, suggests that
other rock types and geological environments will become diamond
targets in the future (Hausel 1996; Erlich and Hausel 2002).
Table 1.
5
Diamond production of major mines in 2001
Country
Carats,
×1000
Amount,
kt
3,685
3,685
144
531
US$/carat
Value, US$
million
Canada
Ekati
Botswana
Jwaneng
12,339
8,920
110
1,357
Orapa
13,056
15,779
50
653
1,021
3,625
180
184
4,977
4,602
85
423
808
6,083
180
145
Finsch
2,465
4,768
70
173
Premier
1,637
3,102
75
123
550
3,766
110
61
65
5,835
400
26
145
2,299
225
33
Letlhakane
South Africa
Venetia
Namaqualand
Kimberley
Baken
Koffiefontein
Russia
Udachnaya
11,500
9,000
85
978
5,500
9,100
65
358
Argyle
26,000
15,100
11
286
Merlin
70
270
110
8
1,385
21,867
220
305
Jubilee
Australia
Namibia
Namdeb Onshore
Adapted from Mining Journal 2002.
The world’s natural diamonds are produced from a small
group of deposits, which typically have operating lives of 20 to 30
years. A notable exception is the Premier mine (South Africa),
which potentially could operate for more than 100 years (Levinson,
Gurney, and Kirkley 1992) (see Table 1).
Africa
The Orange River basin with its many tributaries covers a region
with more than 3,000 known barren and diamondiferous kimberlite
pipes that include some of the richest pipes in the world. The principal diamond-producing countries in Africa are Angola,
Botswana, the Central African Republic, the Democratic Republic
of Congo (formerly Zaire), Ghana, Guinea, Namibia, Sierra Leone,
South Africa, and Zimbabwe. In total, Africa accounts for nearly
50% of the world’s diamond production.
Angola. Angola produces 2 million carats of high-quality diamonds annually derived primarily from alluvial sources. Nearly all
diamond production is derived from alluvial sources in the Andrada
and Lucapa areas of northeastern Lunda Norte and the Cuango
River. Only minor amounts are mined from colluvial and eluvial
deposits overlying kimberlite at the Camafuca–Camazomba intrusive along the Chicapa River near Calonda. Other kimberlites have
been identified in Angola (Janse 1995).
Atlantic Coast. Erosion of diamond pipes and dikes in the
Orange River basin resulted in the concentration of millions of diamonds in the basin and along the Atlantic Ocean shoreline. Stream
sediments in the basin and beach sands along the west coast of
Africa extending from Port Nolloth, Namaqualand, to Luderitz,
Nambia, contain placer diamonds. The powerful energy generated
by the wave action along this coast has destroyed or broken large
numbers of poor-quality stones while gemstones remain intact.
6
Industrial Minerals and Rocks
Botswana. DeBeers discovered three world-class kimberlite
pipes (Orapa, Letlhakane, and Jwaneng) in Botswana between 1967
and 1973. The Orapa pipe was found in 1967 and production began
in 1972. It is the second largest producer of diamonds in the world
and yielded more than 13 million carats in 2001 (Table 1). The
Jwaneng pipe was discovered in 1973 under the sands of the Kalahari
Desert, and mining began on the property in 1982. It has been the
third most productive diamond mine by weight and first by value.
Two smaller pipes known as the Letlhakane 1 and 2 were discovered
in 1968.
Botswana’s diamond reserves are immense. Total production
in 2001 was a record 26.3 million carats, compared to 21.26 million
carats in 1999 and 19.8 million carats in 1998. Output from the
mines was 13 million, 1 million, and 12 million carats from Orapa,
Letlhakane, and Jwaneng, respectively (Table 1). A fourth mine,
Tswapong, produced 10,100 carats in 1999. An application for a
fifth mine at Gope in the Central Kgalagadi Game Reserve was
reviewed in 1999, and Debswana Diamond Company Ltd. (formed
by the Botswanna government and South Africa’s DeBeers in equal
partnership) applied for a license beginning in 2001 to mine diamonds from four small kimberlite pipes known as the B/K pipes
near the Orapa mine.
Central African Republic. Diamonds from the Central African Republic are mined from alluvium. Diamondiferous alluvium
has been found near Bria in the central area of the country; CarnotBerberati in the southwest; and the Mouka Ouadda plateau in the
northeastern portion of the Central African Republic. To date, the
source rocks for the diamonds have not been identified. Production
amounts to about 500,000 carats per year (Janse 1995).
Democratic Republic of Congo. Formerly known as Zaire, the
Democratic Republic of Congo accounts for about 18% of the world
production and, in recent years, has been the second largest producer
by weight, next to Australia. Only 6% of the Congo diamonds, however, are gem quality with another 40% near-gem, resulting in the
Congo being the fourth-ranked producer based on value. According
to the American Museum of Natural History Web site (undated), the
Mbuji-Mayi mine in the Congo has been a prolific source for diamonds with recent annual production of about 5 million carats.
Ghana. Most diamonds in Ghana (formerly known as the
Gold Coast) have been mined from two placers known as the
Akwatia and Birim concessions located northwest of the capital
city of Accra. Annual production peaked at 2,283,000 carats in
1975 and has since declined. About 10% of country’s output is classified as gem quality, and most of the remaining stones are microdiamonds (<2 mm) (Janse 1996). Recoverable resources are
estimated to range between 20 and 50 million carats and Ghana’s
estimated annual production could well exceed 1.3 million carats
(Miller 1995). The Akwatia deposits are nearly depleted, but large
new resources have been identified at the Birim River deposits. One
altered meta-lamproite was found that is thought to represent a primary source for diamonds.
Guinea. Most Guinean diamonds are mined from exceptionally rich gravel placers. Some of the gravel was traced to the
Banankoro kimberlite swarms in eastern Guinea, which consists of
small uneconomic dikes and pipes. Rich placers mined downstream
from the kimberlite swarms were part of the Aredor placer mine
(closed in 1993), and produced a number of large diamonds including several that weighed more than 100 carats; the largest was the
Guinean Star, weighing 255.6 carats (Janse 1995).
Ivory Coast. Also known as Côte d’Ivoire, Ivory Coast produces a small number of diamonds annually from alluvial deposits
and dikes in the Seguela area in the western portion of the country.
Alluvial deposits in the Toritya field in central Ivory Coast also pro-
duce a limited number. The source of many diamonds for the Seguela placers is the Toubabouko olivine lamproite dike. Another
dike, the Bobi lamproite, has yielded about 400,000 carats from the
rock and overlying eluvial deposits (Mitchell and Bergman 1991;
Janse 1996).
Lesotho. Several kimberlites were found in Lesotho (formerly
Basutoland) but production is limited. Two pipes, the Kao and the
Letseng-la-Terai kimberlites, are apparently low grade. The Letseng pipe, however, operated as a commercial mine from 1977 to
1982 and produced some large stones, including a pale-brown 601carat diamond (Janse 1995).
Liberia. Almost all Liberian diamond production (45% of
which is gem quality) comes from small alluvial diggings around
Gbapa.
Mali. Alluvial diamonds and kimberlite pipes occur near
Kenieba in western Mali, but no commercial diamond deposits have
been identified (Janse 1996).
Namibia. Formerly known as South West Africa, Namibia is
a source for small high-quality diamonds from placers and alluvium. Essentially all of Namibia’s production is derived from alluvial, and coastal and submarine terrace deposits in the
Namaqualand coastal region, which includes the coastal region
from Luderitz to Bogenfels.
Submerged terrace deposits are mined to depths of 100 m
along the coast. These are thought to extend 100 km from shore
along the continental shelf (Janse 1995). The Elizabeth Bay deposit
along the coast 30 km south of Luderitz began production in 1991
and has yielded many very high-quality small diamonds. The
deposit was reported to host 38 Mt of ore averaging 0.066 carats/t.
The Auchas mine, located on the north bank of the Orange River 45
km inland, was reported to contain 12.3 Mt averaging 0.036 carats/
t. Kimberlites in Namibia occur in five different fields; all have
proven to be barren (Janse 1995).
Sierra Leone. Diamonds in Sierra Leone are found in stream
and river placers, and in terraces, off-shore terraces, and also in a
few kimberlites. Many placers have been depleted, although large
high-grade zones are still mined. Kimberlite dikes and two small
pipes were found on the Tongo deposit. The dikes were relatively
rich, but their narrow width made them unfavorable for mining. The
small Koidu pipe (0.4 ha) has an ore grade reported at 1.0 carat/t
and is reported to host a very high occurrence (60%) of gem-quality
stones. Sierra Leone is known for its relatively large, high-quality
placer gemstones, and has produced some very attractive stones
including the Woyie River diamond, which weighs 770 carats.
South Africa. Diamonds were initially reported in South
Africa in the 1860s, and between 1870 and 1871, a great diamond
rush occurred along the Orange River, resulting in discovery of
several deposits (Wagner 1914). South Africa is the fifth largest
producer of diamonds (by value) with annual production of 8 to
10 million carats. In 2001, the South African mines produced
10.65 million carats. The region has produced more than 500 million carats since the 1860s. A high percentage of these have been
gem and near-gem, and South African mines have produced some
of the largest diamonds found in history.
The diamonds occur in kimberlite pipes and dikes and in associated alluvial placers. The largest pipe in South Africa is the 54-ha
Premier. The Premier mine has been the source of some of the
world’s largest diamonds, including the Cullinan, Premier Rose,
Niarchos, Centenary, and Golden Jubilee. The largest diamond ever
found, the fist-size (3,106 carats) Cullinan, was recovered from the
Premier.
The Finsch mine covers 17.9 ha and lies 160 km northwest of
Kimberley. It is one of DeBeers’ seven South African operations.
Diamonds
New South Wales. Alluvial diamonds were initially reported
in New South Wales (NSW) in 1861, and were later found in Queensland (1887), in South Australia (1894), and in Tasmania (1899).
From 1884 to 1922, 167,548 diamonds (with stones weighing as
much as 8 carats) were recovered from alluvium in the Copeton
field, NSW.
The diamonds were found in gravel buried by Tertiary basalt
in an active tectonic environment similar to that of the Urals in Russia, the west coast of the United States, and some Archean greenstone terrains in Canada (Erlich and Hausel 2002; Ayer and Wyman
2003; Kaminsky, Sablukov, and Sablukova 2003). It is thought that
Figure 3.
The Argyle mine
128˚
124˚
Timor
Sea
Indian
Ocean
Kimberley
Block
18˚
Kin
Mo g L
bil eop
e o
nn Zone ld
Canning Basin
ar
d
Argyle
E
C
Zo
ne
1
ob
ile
3
N
kM
2
Cr
ee
4
Halls Creek
lls
Le
Derby
Fitzroy
Kununurra
Ha
King
Sound
elf
Australia
Courtesy of W.D. Hausel.
Sh
Discovered in 1961, the deposit was initially developed by open pit.
Since 1991, underground mine operations continued beneath the
abandoned pit. Production from the mine in 2001 was 2.46 million
carats from 4.8 Mt of ore (51.7 carats/100 t).
Diamond-bearing gravels were discovered as early as 1903,
close to the Limpopo River, 35 km northeast of the present location
of the Venetia mine in South Africa. In 1969, DeBeers launched a
reconnaissance sampling program to locate the source of the alluvial deposits, and kimberlite pipes were discovered upstream in
1980. Mine construction began in 1990, and the Venetia mine
opened in 1992, with full production in 1993. This mine represents
one of DeBeers’ single largest investments in South Africa. Situated 80 km from Messina in the Northern Province, the property
required a capital investment of $400 million. The mine produced
4.98 million carats from 4.6 Mt of ore in 2001 (108 carats/100 t).
There are 12 kimberlites in the Venetia cluster. Of the 11 pipes
and 1 dike, only two kimberlites, K1 and K2, are currently being
mined. Some of the pipes were formed by multiple intrusive
events, resulting in a variety of kimberlite facies. The kimberlites
are clustered over approximately 3 km, and the total surface area
of kimberlite is 28 ha. Venetia is being mined by conventional
open pit. Surface mining is expected to continue for 20 years with
the targeted pit depth of 400 m.
Swaziland. One small commercial operation is reported in
Swaziland. Janse (1995) describes an alluvial deposit referred to as
the Hlane occurring downstream from the small (2.8 ha) Dokolwayo kimberlite pipe. The placer has produced about 50,000 carats/
year since 1983.
Tanzania. Diamonds were initially found in alluvial deposits
and later in eluvium on the Mabuki kimberlite 60 km south of Lake
Victoria in northern Tanzania. In 1940 another diamondiferous
kimberlite of significance was found 140 km south of Lake Victoria
by an independent Canadian prospector, John Williamson, who
apparently rode a bicycle in his search for diamonds. This pipe, the
largest economic kimberlite ever found, is known as the Mwadui
pipe. The Mwadui is 1,500 m in diameter, covering 146 ha of surface area. The pipe produced some fine pink stones and averaged
more than 500,000 carats annually in the 1960s, with declining production in recent years. DeBeers later discovered hundreds of other
kimberlites in this region; none have been productive (Janse 1996).
Zimbabwe. Formerly known as Rhodesia, Zimbabwe has produced minor amounts of diamonds from alluvium. The first kimberlite found in southern Zimbabwe—named the Colossus pipe—was
discovered near Lochard in 1907. The pipe was reported to be 1 km
in diameter (Wagner 1971). Janse (1995), however, indicated the
kimberlite to be considerably smaller (900 by 150 m) and not viable.
Other kimberlites were found but all proved to be unprofitable with
the exception of the River Ranch kimberlite, discovered in 1975. A
mine was officially opened there in 1995, but production was minimal and operations ceased in 1998 (Janse 1995).
7
Trou
Proterozoic Mobile Belt
gh
Anticline
Kimberlite
Syncline
Olivine lamporite
Fault
Laucite Lamporite
Concealed Fault
Diamond Occurrence
20˚
Source: Skinner et al. 1985; reprinted with permission of the Geological
Society of South Africa.
Figure 4. The Kimberley block, Western Australia, showing
locations of kimberlites, lamproites, diamonds, the Ellendale
field (E), Calwynyardah field (C), and Noonkanbah field (N)
the diamonds were derived from phreatomagmatic volcaniclastics
and tuffs associated with lamprophyre pipes (Atkinson and Smith
1995). Diamonds in such geological terrains provide signatures,
suggesting derivation from a relatively shallow mantle (<80 km)
(Ayer and Wyman 2003).
Northern Territories. Decades after the diamond discoveries
in NSW, Ashton Exploration discovered diamonds in 1976 near Mt.
Percy, West Kimberley, by following a trail of kimberlitic indicator
minerals. The mineral trail led to diamondiferous lamproite in the
Ellendale field (Tertiary). In August 1979, diamonds were found in
Smoke Creek, more than 350 km to the northeast. In October 1979,
the 1.2-billion-year-old (Ga) Argyle lamproite was discovered
(Atkinson and Smith 1995) (Figure 3). Both lamproite fields are
located within Proterozoic mobile belts cratonized about 1.8 Ga
and were tectonically active until the Devonian or later (Jaques
et al. 1982, 1983; Atkinson, Smith, and Boxer 1984) (Figure 4).
8
Industrial Minerals and Rocks
Currently, about 450 lamproites, kimberlites, and lamprophyres
have been identified in Australia, of which more than 180 are diamondiferous. Some of the recently discovered kimberlites yielded
minor to significant diamond grades (Berryman et al. 1999).
Production began in the mid-1980s at the Argyle mine, and
Australia became a leading diamond producer. At full production,
the mine yielded more than 30% of the world’s annual production.
Further development of the open pit continued into 2001, and the
current operator (Rio Tinto) reported plans to expand operations
underground.
Diamonds were recovered from the Normandy Bow River
placer mine in the lower reaches of Limestone Creek, 20 km northeast of the Argyle. This deposit was discovered in the early 1980s
and mined by Poseidon/Freeport and Normandy from 1988 until
late 1995 (Biggs and Garlick 1987). The plant was inactive at the
end of late 1995, after nearly 7 million carats were produced from
24 Mt of gravel.
Kimberley Diamond Company acquired the Ellendale leases
previously held by Argyle Diamond Mines. Initial bulk sampling
results from Ellendale 4 and 9 revealed higher ore grades near the
surface. The company reported the Ellendale 4 resource at more
than 2 million carats to a depth of 140 m (23 Mt at 0.088 carats/t),
which included a higher-grade zone (444,000 t at 0.261 carats/t) to
a depth of 3 m. The near-surface enrichment zone was part of the
mining target for 2002. Primary diamond resources of Ellendale 4
and 9 were estimated at more than 2.6 million carats.
For the first 3 years of operation, 2.2 Mt of ore was expected
to be mined from the top 3 m of enriched material on both Ellendale 4 and 9. The ore was estimated to average 0.15 carat/t. The
company also reported the discovery of 11 previously unknown
lamproite pipes in the area (Shigley, Chapman, and Ellison 2001).
The Merlin mine, which was developed on a group of 12 diamondiferous kimberlites in northern Australia, yielded the country’s
largest diamond, the 104.73-carat Jungiila Bunajina (“star meteorite
dreaming stone”) white diamond. Merlin is located 80 km south of
Borroloola. After 6 years of production, the mine closed in 2002
because of marginal ore.
Australia’s total diamond production in 2001 was 26.2 million carats, a decrease of 0.4 million carats from the previous year.
The Argyle mine (26.1 million carats) accounted for nearly all of
the Australian production. At one point, Argyle mined nearly 40%
of the world’s annual diamonds: by the end of 2000, the mine had
produced an extraordinary 558 million carats (Shigley, Chapman,
and Ellison 2001). The Merlin mine in the Northern Territory produced 55,000 carats, making it the second largest Australian producer in 2001.
Brazil
A diamond rush occurred in Brazil in 1725, and by the end of 1729,
several diamond placers had been found in eastern Brazil in the
region of Diamantina (“diamond city”). Placers were also found
along the Sao Francisco, Parana, Goyas, and other streams in southeastern Brazil.
In 1844, rich diamond placers were found in another region of
Brazil—the state of Bahia to the north. During the first 120 years of
mining, about 10 million carats were recovered, including some
stones weighing more than 100 carats.
The primary source of the diamonds has not been found, and it
was initially assumed that a rock referred to as itacolumite (micaceous sandstone) was the source. This assumption was based on the
presence of middle Proterozoic diamondiferous conglomerates that
have supported some small mining operations in the Diamantina
Area.
The large number of diamonds found in placers suggests that
major primary diamond deposits will be found in Brazil some day.
Since 1967, a systematic exploration program identified more than
300 kimberlite, lamproite, kamafugite, and melilitite intrusives,
none of which contain economic amounts of diamond (Bizzi et al.
1994; Meyer et al. 1994). A total of about 55 million carats have
been recovered from Brazil, with annual production averaging
about 1.2 million carats.
China
Diamond deposits in Liaoning Province in China are associated
with kimberlite. More than 100 kimberlites are found in this region,
including the Jingangshi Kimberlite, which contains commercial
amounts of diamond (Sunagawa 1990). At another locality, the
Changma mine in Shandong Province near Mengyin, about 500 km
southeast of Beijing, is China’s largest diamond producer. This
deposit was initially mined as an open pit over the past several
decades and converted to underground mining in 2002, with an
expected life of another 30 years. The Changma deposit consists of
two kimberlite diatremes and a dike that all merge at 40 m below
the surface. The kimberlite has been drilled to depths of 600 m.
Production from the mine during the past 30 years included 1.6 million carats recovered from ore that averaged 1.27 carats/t; the largest diamond was a 119-carat stone. The property has an indicated
resource of 1.4 Mt of ore at a grade of 0.92 carats/t with an inferred
resource of 1.5 Mt of 0.63 carats/t. The Changma property includes
nine diamondiferous kimberlites with a total measured and indicated resource of 9.7 Mt at an average grade of 0.055 carats/t
(Beales 2004).
India
Diamonds were reported in the Golconda region of India from
medieval time to the nineteenth century. Golconda was actually the
marketplace, and the source of the diamonds were placers in the
Penner, Karnool, Godvari, and Makhnadi rivers in the Krishna Valley, and possibly in the Panna diamond field to the north in southcentral India (Mathur 1982). Many of the better diamonds ended up
in the royal treasuries of sultans and shahs of India and Persia. Total
production is estimated at about 12 million carats (Milashev 1989).
The majority of the diamonds was found in placer deposits
(Sakuntala and Brahman 1984), although diamonds were also
found in the Majhagawan lamproite as early as 1827. After kimberlite was described in South Africa in 1877, intensive exploration in
the ancient diamond-producing areas of India resulted in the discovery of what was thought to be kimberlite in areas adjacent to
many placers (e.g., Majhagawan and Hinota near the Panna placer
district, and the Wajakurnur and other intrusives in the Anantpur
District). Years later, petrographic studies of some Indian kimberlites confirmed that many were actually olivine lamproite (e.g.,
Majhagawan and Chelima) (Scott-Smith 1989; Middlemost and
Paul 1984; Rock et al. 1992). Diamonds recovered from the pipes
are mostly transparent and flawless, with dominantly octahedral
and dodecahedral habits. About 40% are gem quality (ore grade
~0.01 carats/t).
Mitchell and Bergman (1991) indicated that there are several
other lamproites, kimberlites, and peridotites in this region, and
Rock and others (1992) also reported several olivine lamprophyres
and minettes of potential economic interest in eastern India. Known
kimberlites in India are primarily Proterozoic in age and include diamondiferous kimberlites in the Wajrakarur field in the Andhra
Pradesh of the southern kimberlite province and kimberlites in the
Raipur field in southeastern Madhya Pradesh in the central province
(Middlemost and Paul 1984).
Diamonds
9
Many of the Indian deposits were depleted by the nineteenth
century and new deposits were discovered in the mid-twentieth
century, including placers in the Junkel region and Koel Valley,
and in the Simla region near the Himalayas (which were originally
described in Sanskrit texts). Total historical production is estimated to be between 14 and 21 million carats. Currently, about
20,000 carats are produced each year.
120˚W
112˚
108˚
68˚N
Coronation
Gulf
68˚N
Bathurst
Inlet
Artic
Circle
North America
There is little doubt that Canada, which has become a major diamond producer, will remain in the forefront of diamond production
and exploration for decades to come. Recent exploration in Canada
has resulted in the discovery of more than 500 kimberlites (including some unconventional host rocks), of which nearly half are diamondiferous (Kjarsgaard and Levinson 2002). Some of the
unconventional host rocks include lamprophyre (including
minette) and actinolite schist at Wawa, Canada, that is interpreted
to represent metamorphosed komatiite.
The North American craton is the largest in the world. The cratonic basement rocks of Canada continue south into the United States
and underlie large parts of Montana–Wyoming and the Great Lakes
region. Exploration in the United States, however, has been relatively
minimal. Even so, more than 100 kimberlites, lamproites, and lamprophyres have been identified in the southern extension of the North
American craton in Colorado, Wyoming, and Montana. Approximately half of the kimberlites found in Colorado and Wyoming are
diamondiferous; only one in Montana has yielded diamonds to date.
One mine was developed along the edge of the Wyoming craton in
1995–1996. The Kelsey Lake mine in the Colorado–Wyoming State
Line District south of Laramie, Wyoming, contained low-grade ore
(about 0.05 carats/t) and yielded some high-quality diamonds weighing as much as 28.3 carats (Coopersmith, Mitchell, and Hausel
2003). Mine operations ended because of legal problems.
The presence of several hundred kimberlitic indicator mineral
anomalies, several diamonds, and some geophysical and remote
sensing anomalies support the concept that the Wyoming craton has
been intruded by a major swarm of kimberlitic and related intrusives, most of which remain undiscovered. Because a large part of
the Wyoming craton remains unexplored for diamonds, additional
discoveries are expected. In the Great Lakes region, a group of
about 30 kimberlites are reported in the Michigan–Illinois Area
(eight of which contain trace amounts of diamond) (Hausel 1998).
One of the great exploration success stories of the twentieth
century was the discovery of diamonds in the Northwest Territories
of Canada, which sparked the largest claim-staking rush in history
(Krajick 2001). A group of diamondiferous kimberlites were found
nearly 300 km northeast of Yellowknife under a group of shallow
lakes in the Lac de Gras region. Within a few years following the
discovery, BHP commissioned Canada’s first diamond mine in late
1998 (Figure 5). This mine, known as Ekati, is a world-class mine.
The mine property includes a group of 121 kimberlite intrusives, and
to date, commercial mineralization has been identified and reserves
established for the Fox, Leslie, Misery, Koala, Koala North, Panda,
Beartooth, Sable, and Pigeon kimberlites on the Ekati property; the
other kimberlites are being evaluated for reserves. The mine is anticipated to have a minimum life of at least 25 years.
In 2001, Ekati produced 3.7 million carats, totaling about 6%
of the world’s diamond value. In 2003, production increased to
6.96 million carats (Anon. 2004). The open-pit operation on the
Panda kimberlite reached its maximum economic depth in 2003,
5 years after mining was initiated. The declining production from
the Panda open pit, however, was replaced by production from the
nearby Misery and Koala open pits. Evaluation showed that the
116˚W
Victoria
Island
Great
Bear
Lake
Takijuo
Lake
Conwoyto
Lake
Jericho
Point
Lake
Lac
de Gras
64˚N
Ekati
Aylmer
Lake
Diavik
64˚N
MacKay
Lake
Snap Lake
Yellowknife
Great
Slave
Lake
Kennedy Lake
Advanced
Diamond Project
0
100
200
Kilometers
Northwest Territories
62˚
ewan
Saskatch
Source: Goepel McDermid Securities 1999; reprinted with permission from
Robert W. Klassen.
Figure 5.
Important diamond localities in Canada
Panda kimberlite mine life could be extended using underground
mining techniques; thus, the remaining kimberlite is being developed using sublevel retreat mining. Underground mining was previously initiated at the adjacent Koala North pipe in 2002. The
Panda underground mine is expected to produce 4.7 million carats
over an operating period of 6 years, with production scheduled to
begin in 2005, followed by full production in 2006. The Ekati production for the first quarter of 2004 totaled 1.27 million carats of
diamonds, which was a 40% decline from the previous quarter. For
the first 9 months of fiscal year 2004, the Ekati mine produced
more than 5.3 million carats.
Ore reserves at the Ekati mine are substantial. On June 30,
2003, the Ekati mine reported 47.7 Mt of ore reserves graded at
0.8 carats/t (36.6 million carats of recoverable diamonds) based on
a 2-mm cutoff size. Measured, indicated, and inferred kimberlite
resources stood at 127.9 Mt of ore containing an estimated
171.2 million carats (Robertson 2004). As exploration continues on
the property, these reserves will increase.
A few other commercial properties have been identified in the
Northwest Territories, and several other properties are being
explored or evaluated for reserves. These include Snap Lake, Diavik, and Jericho.
Production at the Diavik mine began in 2003. The Diavik
pipes located in the Lac de Gras region east of Ekati are being
mined by Diavik Diamond Mines based at Yellowknife (Figure 5).
Diavik Diamond Mines is a subsidiary of London-based Rio Tinto,
and the mine is a joint venture between Rio Tinto (60%) and Toronto-based Aber Diamond Mines (40%). Rio Tinto assumed operating responsibility from their subsidiary, Kennecott Canada
Exploration. The deposit is estimated to contain 138 million carats
of diamond and includes four kimberlites (A154S, A154N, A418,
and A21). The A154S kimberlite is one of the richest kimberlites in
the world and contains a reserve of 11.7 million carats at an average grade of 5.2 carats/t. The property is anticipated to yield 6 to
10
Industrial Minerals and Rocks
8 million carats/year when in full production and has reserves that
will sustain the operation for 16 to 22 years. The property lies on a
20-km2 island known as East Island, 300 km northeast of Yellowknife. The Diavik kimberlites (55 million years old [Ma])
intruded the Precambrian basement complex (2.5 to 2.7 Ga).
The Snap Lake mine is located in a kimberlite dike about
100 km south-southeast of Ekati and 220 km northeast of Yellowknife. Snap Lake will be DeBeers’ first mine developed outside
of southern Africa and is anticipated to begin production in 2006,
or possibly as late as 2008. The kimberlite will be mined entirely
underground. The kimberlite is estimated to contain 38.8 million
carats with an average ore grade of 1.46 carats/t.
Toronto-based Tahera Diamond Corporation is the operator of
the Jericho project, located about 170 km north of Ekati near Echo
Bay’s Lupin gold mine. This property includes six diamondiferous
kimberlites within the Nunavut Territory. When placed into production, the property will produce about 6 million carats over a mine
life of 8 years. Reserves of 2.6 Mt of ore averaging 1.2 carats/t have
been established. The mine is expected to begin development in
2004 and production is scheduled for 2005 (Anon. 2004).
Another project of DeBeers Canada—the Victor Project—lies
in the James Bay Lowlands. Victor is one of 18 kimberlite pipes
discovered on the property, 16 of which are diamondiferous. The
Victor kimberlite has a surface area of 15 ha and consists of two
pipes, known as the Victror Main pipe and Victor Southwest pipe,
that coalesce at the surface. The Victor kimberlite is a complex pipe
consisting of pyroclastic crater and hypabyssal facies kimberlite
and has highly variable diamond grades. If a decision is made to put
the property in production, the open-pit mine will have a life of
12 years and total project life of 17 years. The proposed mine would
be supported by a processing plant designed to process 2.5 Mtpy.
DeBeers is also involved in the Kennady (Gahcho Kue) Lake
project, about 100 km east of Snap Lake near Ft. Defiance and
southeast of Ekati. Kennady Lake is under exploration by a joint
venture between Mountain Lake Resources and DeBeers. The property includes the 5034, Hearne, and Tuzo kimberlites. Initial sampling of the 5034 and Hearne pipes yielded an average ore grade of
1.67 carats/t. If this project receives a go-ahead, it is expected that
permitting will require 2 to 3 years followed by another 3 years of
mine development (Anon. 2004).
Since the 1990s, many other deposits have been found in
Canada in the Northwest Territories, Nunavut, Alberta, Ontario,
Quebec, and Saskatchewan (Olson 2001).
According to Engineering and Mining Journal (Anon. 2004),
Canada is currently supplying about 15% of the world’s diamonds
and is expected to show dramatic increases in the future. In 2002,
the Canadian diamond industry produced nearly 5 million carats. In
2003, production increased to 11.2 million carats, and it is estimated that essentially 50% of the world diamond exploration funding is focused on Canada.
Russia
The official discovery of kimberlite in Russia occurred in 1954 at
what later became known as the Mir pipe (Erlich and Hausel 2002).
In 1957, development began on placers associated with the Mir
pipe and was followed by open-pit operations in the kimberlite.
Years later, operations ceased at a depth of 340 m. The average ore
grade was high in the upper mine levels (4.0 carats/t) but decreased
near the bottom of the pit (1.50 to 2.0 carats/t). The Mir had high
gem to industrial diamond content and was the source of several
large gems, including the Star of Yakutia (232 carats) and the Diamond of 26th Party Congress (342.57 carats). Annual output from
the mine was 6.0 million carats (Miller 1995).
The Udachnaya pipe was found in 1955, and mining began on
the associated placers in 1957, followed by open-pit operations in
the pipe. Udachnaya has been the most productive diamond mine in
Russia with more than 14.4 million carats mined, of which 80%
were gems. By 1956, over 500 kimberlites had been discovered in
the former U.S.S.R. During the next 30 years, Russia became the
third largest producer in the world: nearly all its production came
from mines within the northern Siberian platform.
In 1960, the Aikhal pipe was discovered in Yakutia, where
mining began in 1962 and ceased sometime between 1981 and
1988, presumably because of overproduction from other sources.
Production resumed after 1988, and by 1995 the pit reached a final
depth of 240 m. Annual production at the peak of mining was
600,000 carats at an average grade of 1.0 carat/t (Erlich and Hausel
2002).
Another commercial pipe, known as the Sytykanskaya, was discovered in 1955. Open-pit mining began in 1979, and 600,000 carats/
year were produced (average grade of 0.60 carat/t). Another commercial diamond mine, the Internatsional’naya pipe, was found in 1969.
Mining began in 1971 and the open pit was developed to a depth of
280 m by 1980. Open-pit operations ceased, but plans were made to
resume mining underground.
The 23rd Party Congress pipe was discovered in 1959, and
mining on this very rich pipe began in 1966. The ore averaged
6.0 carats/t and the open pit reached a depth of 124 m after 15 years
of operation. The Jubilee (Yubileinaya) pipe was discovered in
1975. Following the removal of 70 to 100 m of basalt overburden,
open-pit mining began. The Jubilee was anticipated to replace production from the declining Udachnaya pipe.
During the 1970s, other diamondiferous kimberlites were discovered within the Russian platform. At about the same time, several kimberlitic pipes were discovered northeast of the city of
Arkhangel’sk, which included the Lomonosov diamond deposit.
Currently, Russia is the fourth largest producer of diamonds in the
world (by weight). The American Museum of Natural History
Nature of Diamonds exhibit in New York City reported that the
country has produced a total of 332 million carats and currently has
an annual production of 10 to 12.5 million carats.
Venezuela
In 1890 and 1901, secondary placer deposits were discovered in
Venezuela and Guyana, and near the end of the 1960s, a placer
deposit was found on Caroni River in southeastern Venezuela. To
mid-1969, 1.3 million carats had been mined; the largest stone
weighed 12 carats. In September 1971, near the town of Salvacion
in the state of Bolivar, another significant placer was discovered.
Within a short period, monthly diamond production from the Salvacion region reached 50,000 carats, but the source of the diamonds
remains unknown.
Other Cratons
Several diamondiferous pipes have been reported in other cratons
such as in the Greenland region, and also in Kazakhstan. Kazakhstan also has the added attraction of having some very unusual and
very rich unconventional metamorphic diamond deposits—but
most of the diamonds are small, low-value industrial microdiamonds (Erlich and Hausel 2002).
EXPLORATION
Cost figures for annual diamond exploration amounts to tens of
millions of dollars. Capitalization costs for the development of the
Ekati diamond mine in the Northwest Territories alone were more
than US$800 million. Regional circumstances will dictate which
Diamonds
exploration method will need to be used; however, when an exploration program begins, priority is given to areas of favorability for
finding “traditional” diamondiferous host rocks. For example, commercial diamondiferous kimberlites are considered to be restricted
to cratonic regions that have been relatively stable for about 1.5 Ga.
Janse (1984, 1994) suggested that cratons be separated into areas of
favorability known as Archons, Protons, and Tectons. This method
for outlining regions of favorability provides an excellent first
option priority list.
Archons (Archean basement stabilized more than 2.5 Ga ago)
are considered to have high potential for discovery of commercial
diamond deposits hosted by kimberlite and possibly by lamproite and
lamprophyre. Protons (Early to Middle Proterozoic [2.5 to 1.6 Ga]
basement terrains) have moderate potential for commercial diamond deposits in kimberlite and high potential for similar deposits
in lamproite and possibly lamprophyre. Tectons (Late Proterozoic
[1.6 Ga to 600 Ma] basement terrains) are considered to have low
potential for commercial diamondiferous host rock. Unconventional diamond deposits (such as high-pressure metamorphic complexes, astroblemes, subduction-related complexes, and volcaniclastics) may occur in tectonically active terrains, but the methods
for exploration for these are not well defined.
Following selection of a favorable terrain, topographic and
geological maps, aerial and satellite imagery, and aerial geophysical data are examined. Unusual circular depressions, circular drainage patterns, noteworthy structural trends, and vegetation
anomalies are noted. Geophysics is used to search for distinct
(“bull’s eye”) conductors and magnetic anomalies. Geochemical
data are examined for chromium (Cr), nickel (Ni), magnesium
(Mg), and niobium (Nb) anomalies.
Stream-Sediment Sampling
One of the primary methods used in diamond exploration is a
stream-sediment sampling program designed to search for “kimberlitic indicator minerals” (pyrope garnet, chromian diopside, chromian enstatite, picroilmenite, chromian spinel, and of course
diamond). Diamond targets are small and can range from diatremes
of several hectares to narrow dikes and sills. Diamond-bearing kimberlites and lamproites typically contain abundant soft serpentine
with resistant mantle-derived xenocrysts and xenoliths. The serpentine matrix tends to decompose, releasing distinct, mantle-derived,
kimberlitic indicator minerals into the surrounding environment.
The indicator minerals may be carried downstream for hundreds of
meters or several kilometers, depending on the climatic and geomorphic history of the region. Diamonds, however, are thought to
be carried considerable distances—in some cases, hundreds of kilometers. The indicator minerals can provide a trail leading back to
the source.
In the planning stages of stream-sediment sampling, proposed
sample sites are initially marked in prominent drainages on a topographic map using a sample spacing designed to take advantage of
the region. In arid regions, sample spacing should take advantage of
relatively short transport distances of the indicator minerals. In subarctic to arctic areas (i.e., Canada, Sweden, Russia, etc.), sample
density may be considerably lower, owing to the greater transport
distance and the logistical difficulties of collecting samples. Anomalous areas are then resampled at a greater sample density.
The usual kimberlitic indicator minerals are rare to nonexistent
in lamproite; thus other minerals (zircon, phlogopite, K-richterite,
armalcolite, priderite) may be considered that unfortunately have
low specific gravity and poor resistance to abrasion, and are potentially difficult to identify. The better indicators for diamondiferous
lamproite are diamond and magnesiochromite.
11
To take advantage of the dispersion of kimberlitic indicator
minerals, the size of samples are determined based on the environment. For example, much larger samples are taken where there is a
general lack of active streams compared to regions with active
drainages. In areas with juvenile streams, samples are often panned
on site to recover a few pounds of sample concentrate. Recovered
indicator minerals are tested for chemistry using an electron microprobe to identify those that have higher probability of originating
from the diamond stability field. The data are plotted on maps to
facilitate evaluation.
Geomorphology
Kimberlite and olivine lamproite are often pervasively serpentinized, making outcrops the exception rather than the rule. In many
cases, geomorphic expressions of pipes are subtle to unrecognizable. The Kimberley pipe in South Africa was expressed as a slight
mound, but nearby pipes (i.e., Wesselton pipe) were expressed as
subtle depressions. Others produced subtle modifications of drainage patterns (Mannard 1968). In the subarctic, where glaciation has
scoured the landscape, some kimberlites produce noticeable
depressions filled by lakes. In the semiarid region of Wyoming and
Colorado, a few kimberlites are expressed as slight depressions, but
most blend into the surrounding topography and may or may not
have a subtle vegetation anomaly.
In the Ellendale field, in Western Australia, serpentinized diamondiferous olivine lamproites lie hidden under a thin layer of soil
in a field of well-exposed leucite lamproite volcanoes. The Argyle
lamproite and diamondiferous lamproites in the Murfreesburo Area
of Arkansas were also hidden by a thin soil cover.
Lineaments
Many kimberlites and lamproites are structurally controlled (Hausel, McCallum, and Woodzick 1979; Hausel, Glahn, and Woodzick
1981; Macnae 1979, 1995; Nixon 1981; Atkinson 1989; Erlich and
Hausel 2002). Controlling lineaments and fractures may be indicated by alignment of a cluster of intrusives or by the elongation of
a pipe. In Lesotho, South Africa, Dempster and Richard (1973)
reported a close association of kimberlite with lineaments: 96% of
kimberlites were found along west–northwest trends, and many
pipes were located where the west–northwest trends intersected
west–southwest fractures.
Lamproites in the Leucite Hills, Wyoming, are found on the
flank of the Rock Springs uplift, where distinct east–west fractures
lie perpendicular to the axis of the uplift (Hausel, Gregory, and
Sutherland 1995). In the West Kimberley Province of Western
Australia, some lamproites are spatially associated with the Sandy
Creek shear zone, a Proterozoic fault. In the Ellendale field, several
lamproites lie near cross faults perpendicular to the Oscar Range
trend, even though the intrusions do not appear to be directly
related to any known fault. The Argyle lamproite to the east has an
elongated morphology suggestive of fault control and intrudes a
splay on the Glenhill fault (Jaques, Lewis, and Smith 1986).
Remote Sensing
Kingston (1984) reported that remote-sensing techniques are widely
used to search for kimberlite; these include conventional and false
color aerial photography, Landsat multispectral scanner satellite
data, and airborne multispectral scanning. Multispectral scanning
data are used to identify spectral anomalies related to magnesiumrich clays (i.e., montmorillonite), carbonate, and other material with
low silica content. Image enhancement techniques (contrast
enhancements, ratios, principal components, and clustering) produce images that are optimum for discrimination of kimberlite and
12
Industrial Minerals and Rocks
olivine lamproite soils. These and other photo images can be used to
search for vegetation and structural anomalies. Airborne multispectral scanning provides higher resolution than Landsat and can also
be used to measure reflectance qualities of clay in soil.
Many pipes and dikes possess distinct structural qualities or
vegetation anomalies that may allow detection on aerial photographs. Mannard (1968) reported that kimberlites in southern and
central Africa were identified on aerial photographs on the basis of
vegetation anomalies, circular depressions or mounds, and tonal
differences. Low-level aerial photographs (both conventional and
false color infrared) have been used to locate kimberlite in the
former U.S.S.R. (Barygin 1962) and in the United States (Hausel,
McCallum, and Woodzick 1979; Hausel et al. 2000, 2003).
Geophysical Surveys
Geophysical exploration has been successful in the search for hidden kimberlite and lamproite (Litinskii 1963a, 1963b; Gerryts 1967;
Burley and Greenwood 1972; Hausel, McCallum, and Woodzick
1979; Hausel, Glahn, and Woodzick 1981; Paterson and MacFadyen
1984; Woodzick 1980), particularly in districts where kimberlites
have previously been discovered. Contrasting geophysical properties
are often favorable for distinguishing kimberlite, lamproite, and
minette from country rock.
INPUT airborne surveys are effective in identifying both serpentinized and weathered kimberlite, owing to the combination of
electromagnetics and magnetics used in the survey. Rock exposures
of kimberlite may yield magnetic signatures but are poorly conductive, whereas deeply weathered kimberlites are conductive but
poorly magnetic.
Because of the relatively small size of the diamond host rock,
close flight-line spacing is necessary. In an airborne INPUT survey
over the State Line District, Wyoming, a flight-line spacing of
200 m effectively detected several kimberlites and identified distinct magnetic anomalies interpreted as blind diatremes (Paterson
and MacFadyen 1984). An aeromagnetic (200- to 400-m line spacing) survey flown over parts of northeastern Kansas identified several anomalies, some of which were drilled, resulting in the
discovery of previously unknown kimberlites (i.e., Baldwin Creek,
Tuttle, and Antioch kimberlites) (Berendsen and Weis 2001).
Flight-line spacings of 50 to 100 m were used for INPUT, magnetic, and radiometric surveys in the Ellendale field in Australia
(Atkinson 1989; Janke 1983; Jaques, Lewis, and Smith 1986). The
olivine lamproites yielded distinct dipolar magnetic anomalies.
In Yakutia Province, Russia, ground magnetic surveys were
used where differences between the magnetic susceptibility of kimberlite and the carbonate sedimentary country rock were high. Airborne surveys also successfully detected anomalies as great as
5,000 gammas (Litinskii 1963b). In Mali, West Africa, the magnetic contrast between kimberlite and schist and sandstone country
rock resulted in 2,400-gamma anomalies over kimberlite (Gerryts
1967). In Lesotho, anomalies over kimberlite were comparable
with those in Yakutia Province (Burley and Greenwood 1972).
Fipke and colleagues (1995) indicated that barren peridotite
phases in Arkansas yielded magnetic highs, but the diamondiferous phases were not detected. In northeastern Kansas, Brookins
(1970) reported large positive (550 to 5,000 gamma) and negative
(0 to –2,800 gamma) anomalies over some kimberlites emplaced
in regional sedimentary rocks. The sedimentary rocks had relatively low magnetic susceptibility, making magnetic surveys an
effective method for exploration.
Most kimberlites in the Colorado–Wyoming State Line District yielded small complex dipolar anomalies in the range of 25 to
150 gammas, with some isolated anomalies of 250 and 1,000 gam-
mas (Hausel, McCallum, and Woodzick 1979). Blue ground
(weathered) kimberlite tends to mask magnetic anomalies. In the
Iron Mountain District, where much of the kimberlite is relatively
homogeneous, massive hypabyssal-facies kimberlite, only weak to
indistinct magnetic anomalies were detected (Hausel et al. 2000).
Magnetite is replaced by hematite during weathering, masking
near-surface magnetic affinity. Clay produced during weathering
promotes water retention, thus weathered blue ground over kimberlite may produce vegetation anomalies that are susceptible to detection by electrical methods. For example, resistivity surveys in the
Colorado–Wyoming State Line District detected apparent resistivity of 25 to 75 ohm-m over weathered kimberlite, compared with
150 to 2,250 ohm-m in the country rock granite (Hausel, McCallum, and Woodzick 1979).
Resistivity of weathered lamproite may be lower than that of
country rock, owing to the conductive nature of smectitic clay relative to illite, kaolinite, and other clay minerals (Gerryts 1967; Janke
1983). The Argyle olivine lamproite, however, yielded moderate to
strong resistivity anomalies (40 to 100 ohm-m) compared to the
surrounding country rock (200 ohm-m) (Drew 1986).
Biogeochemical and Geochemical Surveys
Kimberlite and lamproite are potassic alkalic ultrabasic igneous
rocks with elevated barium (Ba), cobalt (Co), Cr, cesium (Cs),
phosphorus (P), lead (Pb), rubidium (Rb), strontium (Sr), tantalum
(Ta), thorium (Th), uranium (U), vanadium (V), and light rare earth
elements (LREE). The elevated Cr, Nb, Ni, and Ta may show up in
nearby soils (Jaques 1998), but dispersion of these metals in soils is
not extensive. Stream-sediment geochemistry generally is not useful because of efficient dispersion of most metals in streams. In the
Colorado–Wyoming State Line District, Cominco American outlined several known kimberlite intrusives on the basis of Cr, Nb,
and Ni soil geochemical anomalies. Dispersion patterns were
restricted, however, and of little use in exploration in this terrain.
Gregory and Tooms (1969) found that Mg, Ni, and Nb anomalies did not extend farther than 0.6 km from the Prairie Creek lamproite, Arkansas. Haebid and Jackson (1986) noted that soil
geochemical anomalies (Co, Cr, Nb, Ni) were detected in sand and
soil immediately above lamproite vents in West Kimberley, Australia. Such anomalies could prove useful in the search for hidden olivine lamproites. Gregory (1984) used lithochemistry to distinguish
olivine lamproite from leucite lamproite on the basis of Mg, Ni, Cr,
and Co ratios.
Bergman (1987) suggested that olivine lamproites are generally enriched in compatible elements relative to leucite lamproites
as a result of the abundance of xenocrystal olivine in the former.
Barren lamproites contain elevated alkali and lithophile contents
(K, sodium [Na], Th, U, yttrium [Y], and zirconium [Zr]) relative to
diamondiferous (olivine) lamproites. Diamondiferous lamproites
possess twice the Co, Cr, Mg, Nb, and Ni and half the aluminum
(Al), K, and Na as barren lamproites (Mitchell and Bergman 1991),
and lamproites have anomalous titanium (Ti), K, Ba, Zr, and Nb
compared to most other rocks. These components may favor the
growth of specific flora or may stress local vegetation (Jaques
1998). The Big Spring vent, West Kimberley, Australia, is characterized by anomalous faint pink tones that reflect the growth pattern
of grass on the vent (Jaques, Lewis, and Smith 1986).
Many kimberlites in the Colorado–Wyoming State Line District will not support growth of woody vegetation, resulting in open
parks over kimberlite in otherwise forested areas. These same kimberlites may support a lush stand of grass delineating the limit of the
intrusive. Distinct grassy vegetation anomalies over kimberlites in
the Iron Mountain District, Wyoming, were used successfully to map
Diamonds
many intrusives (Hausel et al. 2000). The anomalies are especially
distinct after a few days of rain in the late spring.
Some Siberian kimberlites support denser stands of larch
(Larix dahurica) and abundant undergrowth of shrub willow (Salix)
and alder (Alnus) compared to surrounding Cambrian carbonates.
In central India, trees over the Hinota pipe are healthier, taller, and
denser than those in the surrounding quartz arenite. This may be
attributed to greater availability of K, P, micronutrients, and water.
Vegetation over the Sturgeon Lake kimberlite in
Saskatchewan was tested for 48 elements; the kimberlite showed a
consistent spatial relationship with Ni, Sr, Rb, Cr, manganese
(Mn), and Nb, and to a lesser extent with Mg, P, and Ba; relatively
high Ni concentrations occurred in dogwood twigs. In hazelnut
twigs, Cr levels were greater than 15 ppm near the kimberlite but
only 5 to 8 ppm elsewhere, and Nb was higher in hazelnut twigs.
Sr and particularly Rb were relatively enriched in some plant species on kimberlite. The Sr was probably derived from the carbonates associated with the kimberlite, whereas the Rb was derived
from phlogopite. Ni, Rb, and Sr distribution and Cr enrichment
associated with Mn depletion in the twigs could be used to identify
nearby kimberlite.
MINING AND MILLING
Economic diamond deposits depend on the average price of stones,
the amount of waste material removed, mining methods, company
politics, socioeconomics of the area, and many other factors. For
example, a diamond deposit may be mined at a comparatively lower
cost in a developing country because of the availability of an inexpensive labor force, although constructing an infrastructure in such
an area could offset some of these benefits. In the United States,
high labor and mining costs require higher-value ore for commercial operation; however, an infrastructure may already be available.
More than half of the world’s natural diamonds are mined
from kimberlite and lamproite and the rest are mined from placers.
Economic cutoff grades are typically >0.10 carat/t (Jaques 1998),
but the grade is highly dependent on mining costs and the value of
the recovered diamonds. Thus the economic cutoff grade will vary
depending on these factors. Average ore grades range from a high
of 6.8 carats/t for Argyle to a low of about 0.15 carat/t for Prairie
Creek, Arkansas. Some of the rich crater facies lamproite mined at
Argyle yielded grades as high as 20 carats/t. Most economic deposits yield >30% gem-quality diamonds.
Commercial deposits include narrow dikes to pipes of 30 to
1,500 m across. Pipes range in surface area from 1 to 150 ha, averaging about 12 ha (Jaques 1998). Diamond mines possess resources
in the neighborhood of more than 10 Mt to 350 Mt of ore, and the
richest deposits contain reserves measured in the hundreds of millions of carats that are valued in the billions of dollars.
Open-pit diamond mines are typically designed to recover as
little as 100,000 t to more than 10 Mt of ore per year. Annual diamond production may range from several thousand carats to a few
million carats. For example, the Finsch mine, South Africa, produced about 5 million carats annually between 1981 and 1991,
whereas annual diamond production for the extremely rich Argyle
lamproite reached a record 39 million carats during the height of
operation.
Diamond quality and size must also be considered in commercial operations. Lamproites appear to produce small diamonds with
large percentages of colored stones. Many kimberlites yield a large
range in diamonds, including some very large stones. For example,
the average diamond from the Argyle lamproite is small (only
<0.1 carat), and those from Ellendale lamproites are only 0.1 to
0.2 carat (Mitchell and Bergman 1991). The largest reported dia-
13
mond from the Prairie Creek lamproite is 40.42 carats (Hausel
1998). Diamonds from some kimberlites, however, are extraordinary. The largest diamond ever recovered was the size of a human
fist; it was mined from the Premier kimberlite, South Africa, and
weighed 3,106 carats.
Bulk sampling is the initial step in evaluation of a commercial
diamond deposit. If favorable, additional bulk samples are used to
assist in establishing ore grade maps to aid in mine planning. Samples are taken on the surface and from drilling in order to achieve a
three-dimensional view of ore grades. If the pipe is considered to be
economic, planning is completed for an initial open-pit design and a
mill placed near the pipe. Open-pit mining typically proceeds from
a spiral road developed from the rim of the pit toward the center of
the pipe. As mining proceeds, the country rock is cut back in steps
to aid in supporting the highwalls of the open pit. Mining in the pit
may occur in an oval pattern or in a polygonal pattern (Bruton
1979).
As mining continues and the pipe narrows at depth, the open
pit will shrink to smaller and smaller diameters. Mining operations
may ultimately continue underground using bulk recovery by block
caving. Fewer than 30% of diamond mines, however, are continued
underground. And to do so, the diamond ore must be of relatively
high value, because the cost of underground mining is considerably
higher and the amount of ore recovered is considerably lower.
Some kimberlites in Siberia and South Africa have been mined to
depths of 1,080 m. Open pits may have mine lives of 2 to 50 years
(Jaques 1998).
Following recovery of rock mined from open-pit operations,
the ore is crushed and screened. Screening separates midsize from
larger material rejects and from material too small to contain commercial diamonds. Decisions on the maximum screen size must
weigh the cost of processing additional material with the loss of
potentially priceless large diamonds.
The typical diamond mill has a basic flowsheet that begins
with primary milling and continues to primary gravity concentration, secondary concentration, magnetic separation, and attrition
milling. The final diamond extraction stage uses grease tables, electrostatic separation, or x-ray fluorescence extraction (Bruton 1979).
Placer mines are different. The size of a placer mine will vary
from a small, one-person operation to a full-scale mine using bulldozers, scrapers, and dredges. Paystreaks are identified in streams
or beaches; mining is then completed using small-scale or largescale earth-moving equipment (Bruton 1979).
GEMOLOGY
The primary monetary value for diamond is as gemstones. Diamond prices vary considerably. There are approximately 5,000 diamond categories with prices that vary from $0.5/carat up to several
tens of thousands of dollars per carat (for large uncut or colored
fancy diamonds) (Miller 1995). Many faceted diamonds are worth
many times an equivalent weight in gold or platinum. Rough gemstone diamonds have values as high as 100 or more times that of
industrial diamonds. After the diamonds are faceted, the value of
the gem can increase another 10- to 100-fold, and the final placement of a stone in jewelry will again add another increase in the
value of the stone. Thus, any mining operation should consider not
only recovery of the gems but also the fashioning of the gems and
marketing.
Diamonds are one of the more valuable commodities on earth,
and arguably are the most valuable of all commodities based on
weight. For example, some Argyle pink diamonds have sold for
as much as $1 million per carat (one carat weighs only 0.2 g
[0.007 oz]). Thus, an equivalent weight in gold would be worth
14
Industrial Minerals and Rocks
only $2.80 (at $400/oz). The extreme value of diamond is due to its
mystique, rarity, extreme hardness, high refractive index, and dispersion that can result in brilliant gems with distinctive “fire” when
faceted and polished.
Four general types of natural commercial diamonds are recognized. These are gem, bort (poorly crystallized, gray, brown translucent to opaque), ballas (spherical aggregates formed of many
small diamonds), and carbonado (opaque, black to gray, tough, and
compact). Gem diamonds are further subdivided into gem and neargem (low-quality gemstones).
The fashioning of diamond “rough” into a finished gem may
require up to six steps that include marking, grooving, cleaving,
sawing, girdling, and faceting (Hurlbut and Switzer 1979). Whether
or not all of these steps are used depends on the size, shape, and
quality of the rough stone.
The value of finished gem diamonds is judged by the “four
Cs”: cut, clarity, carat weight, and color. The cut of a diamond can
increase its value tremendously, and the better proportioned, polished, and faceted, the greater its value. When the girdle (base) and
table of the diamond are proportioned correctly, the diamond will
exhibit greater fire and brilliance.
Diamonds can be graded using the Gemological Institute of
America’s color-grading system. This ranges from D (colorless) to
X (light yellow). Each letter of the alphabet from D to X shows a
slight increase in yellow tinge that is generally not apparent to the
untrained eye (Hurlbut and Switzer 1979). Fancy diamonds are separated from colorless diamonds into groups based on color and
intensity (Bruton 1978). Clarity is determined by the presence or
absence of blemishes, flaws, and inclusions. One typical grading
system ranges from Fl (flawless) to I3 (imperfect) with intermediate
grades of VVS1 (very, very slightly imperfect), VVS2, VS1, VS2,
SI1, SI2, I1, and I2.
USE
The diamond industry is a multi-billion-dollar mega-industry. The
unique physical and optical properties of diamond also make it
indispensable and irreplaceable for many industrial uses in addition
to personal adornment in jewelry.
Harlow (1998) and Olson (2001, 2003) describe many uses
for industrial diamonds. Because of the mineral’s extreme hardness,
industrial and synthetic diamonds are used extensively as abrasives
in grinding, drilling, cutting, and polishing. Diamond also has
chemical, electrical, optical, and thermal characteristics that make
it the best material available for wear- and corrosion-resistant coatings, special lenses, heat sinks in electrical circuits, wire drawing,
drilling, and many other advanced technologies. One significant
future application will be in computer chips because of the diamond’s unmatched thermal conductivity and resistance to heat. A
tremendous amount of heat can pass through diamond without
causing damage.
Today’s speedy microprocessors run hot—up to 200°F—and
microprocessors cannot run much faster without failing. Diamond
microchips would be able to handle much higher temperatures that
would liquefy ordinary silicon, allowing them to run at higher
speeds. But manufacturers have not considered using the precious
stone because it has never been possible to produce large diamond
wafers affordably. The Florida-based Gemesis and the Bostonbased Apollo Diamond Company plan to use the diamond jewelry
business to finance attempts to introduce diamonds into the
semiconducting world.
At room temperature, diamond is the hardest known material
with the highest thermal conductivity of any substance. Even
though diamond is more expensive than competing abrasive materi-
als such as garnet, corundum, and carborundum, diamond has
proven to be cost-effective in several industrial processes because it
cuts faster and lasts longer than rival material. Synthetic industrial
diamond is superior to natural industrial diamond in that it can be
produced in unlimited quantities and tailored to meet specific applications. Consequently, manufactured diamond accounts for more
than 90% of the industrial diamonds used in the United States.
According to the USGS, much of the synthetic industrial diamond produced domestically has been used as grit and powder
(Olson 2002, 2003). The major uses were in machinery (27%),
mineral services (18%), stone and ceramic products (17%), abrasives (16%), contract construction (13%), transportation equipment
(6%), and miscellaneous uses (3%) (Olson 2002, 2003). Industrial
diamonds are used in the production of computer chips; in construction; in the manufacture of machinery; for mineral and energy
exploration and mining, stone cutting and polishing; and in transportation (infrastructure and vehicles). Stone cutting, along with
highway construction and repair, are some of the largest users of
industrial diamond.
Diamond has one significant limitation in industrial use: it
reacts with iron at high temperature, causing the diamond to revert
to graphite, which results in high rates of wear. In an iron-rich environment, diamond may be uneconomical to use in comparison to
other conventional abrasives (i.e., aluminum oxide, silicon carbide,
and boron nitride). Even though these are considerably softer than
diamond, they are suitable as high-performance abrasives on ferrous work-pieces.
Diamond use has increased in both jewelry and industrial applications. One reason for the increase is the development of diamond
synthesis technology, making it possible to produce diamond abrasives for specific applications. In the past, the only option was to use
natural diamond, which had to be sorted by size and crushed, or by
surface treatment such as rounding. Synthetic diamond abrasives,
however, can now be produced under a controlled environment such
that the shape of the crystal can be made irregular and sharp.
Diamond has many potential exotic applications. For example, the Venus probe was fitted with a transparent diamond window
because diamond was the only material transparent to infrared light
that could withstand the extreme cold and vacuum of space and the
extreme high temperatures and atmospheric pressures of Venus’s
atmosphere (up to 920°F, and pressures a hundred times that of
Earth) (Ward 1979). Another exotic use gives new meaning to the
family jewels. LifeGem in Illinois started manufacturing diamonds
from cremated human ashes for jewelry for surviving relatives. The
cost for a “family jewel” is reported to be more than $2,000 for a
0.25-carat stone.
Diamond has applications in high-energy physics. Diamond
windows are used in high-power lasers because of the high thermal
conductivity, low absorption coefficient, and low value of temperature coefficient of refractive index. Diamond anvils are used in
high-pressure research, where pressures greater than 4 megabars
are needed. Such ultra-high-pressure research can simulate conditions in the core of the earth and on other planets.
Diamonds are also used in dental drills and surgical blades,
and provide cutting edges that are many times sharper than the best
steel blades. Since diamond has the greatest thermal conductivity of
any material, pinhead-size gold-coated diamonds are used in highcapacity miniature transmitters that carry television and telephone
signals.
Synthetics
Synthetic gem diamonds and simulants are becoming more common in the marketplace. These include cubic zirconia and moissan-
Diamonds
ite. Moissanite has twice the fire of natural diamond, is doubly
refracting (unlike diamond and cubic zirconia, which are singly
refractive), and has a hardness of 9.25—thus, both moissanite and
cubic zirconia can easily be scratched by diamond. Double refraction is detectable in moissanite when viewing the front of the stone.
The back facets will appear to be duplicated because of the double
refraction—except when viewing down the optic axis where light is
singly refractive. The optic axis is usually perpendicular to the table
of moissanite; thus, one must observe the back facets through
another facet to see evidence of double refraction.
Synthetic gem-quality diamonds can be produced in about
24 hours. Some stones weighing up to 3 carats have been produced
for a few hundred dollars (uncut). Most are yellow, but some Russian stones are clear. In 1971, General Electric grew facet-quality
synthetic diamonds that were nearly colorless (0.3 and 0.26 carats).
The colorless gemstones caused concern in the jewelry trade.
Diamond simulants can be detected by a simple thermal conductivity test, but most jewelers were unprepared to distinguish faceted
synthetic diamond from natural faceted diamond. Thus, DeBeers
developed a diamond verification instrument known as DiamondView, which uses UV fluorescence to distinguish colorless natural
diamond from synthetic diamond. In addition, many synthetic diamonds examined by the Gemological Institute of America contain
metallic inclusions in high enough abundance that they are able to
attract a magnet. Nonfaceted synthetic diamonds exhibit a unique
crystal habit of a cuboctohedron with a flat base. Synthetic diamonds also exhibit unusual dendritic and striated surface patterns.
According to Shigley and others (1997), because of the technological challenges and high cost of production, it is unlikely that fashioned gem-quality diamonds larger than 25 points will affect the
gemstone industry in commercial quantities.
FUTURE OF THE DIAMOND INDUSTRY
Diamonds have intrinsic value because of unique hardness, transparency, and thermal conductivity. Diamonds will be needed as
long as there are industrialized nations. Without any foreseeable
major economic disasters, the future of the diamond industry
should remain strong.
As science and industry advance, additional applications for
diamond are likely to be found in the electronics industry. Demand
for diamonds for drilling in exploration for oil, gas, and minerals,
and in the construction industries, is anticipated to increase. Some
technological advances will demand both natural and synthetic diamond in the future.
For many years, the gem diamond industry was controlled by
DeBeers—a monopoly so powerful that the diamond industry and
DeBeers were thought by many to be the same. But the discovery of
significant diamond resources outside of Africa has diminished
DeBeers’s control over the diamond market.
The first real threat to the monopoly occurred with the discovery of significant gem-quality diamond deposits in the former
U.S.S.R. in the 1950s, but communistic bureaucracy could not compete with South Africa, and the Soviet diamonds did not greatly
affect the market (Erlich and Hausel 2002). A major diamond discovery (Argyle) in Western Australia in the 1980s started the real
first erosion of the monopoly. The Argyle deposit, however, though
rich in diamonds, was dominated by industrial stones, and the gemstones recovered from the mine were small. Even so, the Australian
company, Ashton Mining, decided to market their own production.
Some gemstones produced by Argyle included rare pink diamonds. Marketing strategies by the Australians were brilliant,
resulting in the Argyle pinks becoming some of the more valuable
gemstones on Earth. A large population of the Argyle diamonds
15
was also light-brown to brown and had been considered by the jewelry trade as industrial or near-gem. These were marketed as champagne and cognac diamonds, and the marketing strategy effectively
resulted in these stones becoming highly sought gemstones. Even
so, many of the Argyle diamonds were small and required the special cutting skills of gem cutters in India and Sri Lanka.
The next major diamond discoveries were made on the North
American craton. This is the largest craton, with the largest Archon
core, in the world. Based on the sheer size of the craton, and the
many finds of detrital diamonds in glacial moraines, this craton
should have been a high-priority target for diamond exploration
groups. But for many years, the North American craton was
ignored.
The discovery of economic diamond deposits in this craton
was the result of unrelenting prospecting by a small group of geologists (Krajick 2001). The discovery set off the greatest rush in modern history and resulted in the development of a diamond industry
in Canada.
Diamond production began in Canada following the capitalization of BHP’s Ekati mine at more than $800 million. A few other
mines have now been developed, and in April 2004, the value of
diamond production from Canada surpassed that of South Africa.
This occurred in 6 years. In the future, many more discoveries of
diamondiferous kimberlite can be expected in the North American
craton. To date, as many as 500 kimberlites and some unconventional host rocks have been identified in Canada—early reports are
that 50% contain diamonds—which could easily make the North
American craton the primary source of diamonds in the near future.
The North American craton extends across the Canadian border into the United States, where several diamond deposits have
been found. Even so, much of the terrain in the United States has
not been prospected, or was only partially explored for diamonds.
Many exploration targets remain inexplicably unexplored. To date,
only two deposits have been mined for diamonds in the United
States—one in the Colorado–Wyoming State Line District, and
another near Murfreesburo, Arkansas.
Diamond exploration in the near future will continue to focus
on Canada, where the geology and political climate are favorable.
In addition to discoveries of diamonds in kimberlite and some lamproites, one might anticipate additional diamond discoveries in
some unconventional host rocks such as minettes, alnoites, other
lamprophyres, komatiites, and in particular, subduction-zonerelated breccias.
One concern that has arisen is the potential production of
relatively inexpensive synthetic gem-quality diamonds. Natural
gem-quality diamonds, however, are also relatively inexpensive
until they are faceted and mounted in jewelry. And it is human
nature to want a natural gem rather than a synthetic stone or imitation. Gem-quality synthetic diamonds will probably not greatly
affect the jewelry market.
CONCLUSION
With the current trend of investment, exploration, and progressive
pro-mining atmosphere, it is anticipated that Canada will be a leading diamond producer for decades to come. The sheer size of the
North American craton allows one to predict Canada to become the
world’s primary source for diamonds in the future. Unless there is a
major change in attitude of the U.S. government and the population,
little is expected to be produced in the United States, even though
parts of the country are underlain by this craton. The importance of
the North American craton in the future of the diamond industry
has resulted in investments of hundreds of millions of dollars in
exploration in North America.
16
Industrial Minerals and Rocks
BIBLIOGRAPHY
American Museum of Natural History, undated. Web site. Available
from http://www.ny.com/cgibin/frame.cgi?url=http://www.amnh.
org/&frame=/frame/museums.html.
Anon. 2004. Canadian diamonds—an update. Engineering and
Mining Journal 206(6):27–28.
———. 2005. Canada’s Diamond Age (1990–2005). Northern
Miner 9:1–5.
Atkinson, W.J. 1989. Diamond exploration philosophy, practice,
and promises: A review. Pages 1075–1107 in Proceedings of the
4th International Kimberlite Conference. Volume 2, Kimberlite
and Related Rocks: Their Mantle-Crust Setting, Diamonds, and
Diamond Exploration. Edited by J. Ross, A.L. Jaques, J.
Ferguson, D.H. Green, S.Y. O’Reilly, R.V. Duncan, and A.J.A.
Janse. Special Publication 14. Victoria, Australia: Blackwell
Scientific Publications.
Atkinson, W.J., and C.B. Smith. 1995. Diamond deposits in
Australia. SME Preprint No. 95-217. Littleton, CO: SME.
Atkinson, W.J., C.B. Smith, and G.L. Boxer. 1984. The discovery
and evaluation of the Ellendale and Argyle lamproite diamond
deposits, Kimberley region, Western Australia. Pages 121–134
in Applied Mining Geology, Problems of Sampling and Grade
Control. Edited by R.A. Metz. New York: AIME.
Ayer, J.A., and D.A. Wyman. 2003. Origin of diamondiferous
Archean lamprophyres in the evolution of the Michipicoten and
Abitibi greenstone belts. Page 137 in Proceedings of the 8th
International Kimberlite Conference. Program with Abstracts.
Vancouver: Lithos.
Barygin, V.M. 1962. Prospecting for kimberlite pipes from the air.
Mining Magazine 107(2):73–78.
Beales, P. 2004. China diamond boosts output at 701 mine. The
Northern Miner May 10: B3.
Berendsen, P., and T. Weis. 2001. New kimberlite discoveries in
Kansas: Magnetic expression and structural setting.
Transactions, Kansas Academy of Science 104(3–4):223–236.
Bergman, S.G. 1987. Lamproites and other potassium-rich igneous
rocks: A review of their occurrence, mineralogy and
geochemistry. Pages 103–190 in Alkaline Igneous Rocks. Edited
by J.G. Fitton and B.G.J. Upton. Special Publication 30.
London: Geological Society.
Berryman, A.K., J. Steinhofer, S.R. Shee, B.A. Wyatt, and E.A.
Belousova. 1999. The discovery and geology of Timber Creek
Kimberlites, Northern Territory, Australia. Pages 30–39 in
Proceedings of the 7th International Kimberlite Conference.
Edited by J.J. Gurney, M.D. Pascoe, and S. H. Richardson. Cape
Town, South Africa: Red Roof Design.
Biggs, E.R., and H.J. Garlick. 1987. Bow River Project.
Independent Geologists’ report in prospectus for FreeportMcMoRan Australia Limited. Perth, Australia: Freeport
McMoRan.
Bizzi, L.A., C.D. Smith, M.J. deWit, R.A. Armstrong, and H.O.A.
Meyer. 1994. Mesozoic kimberlites and related alkalic rocks in
the southwestern Sao Francisco Craton, Brazil. Pages 156–171
in Proceedings of the 5th International Kimberlite Conference.
Special Publication 1/A. Rio de Janeiro: Companhia de
Pesquisa de Recursos Minerais.
Brookins, D.G. 1970. Kimberlite at Winkler Crater, Kansas.
Geological Society of America Bulletin 81:241–246.
Bruton, E. 1979. Diamonds. Radnor, PA: Chilton Book Company.
Bundy, F.P., and J.S. Kasper. 1967. Hexagonal diamond, a new
form of carbon: Journal of Chemical Physics 46(9):3437–3446.
Burley, A.J., and P.G. Greenwood. 1972. Geophysical Surveys over
Kimberlite Pipes in Lesotho. London: Institute of Geological
Sciences.
Coopersmith, H.C., R.H. Mitchell, and W.D. Hausel. 2003.
Kimberlites and lamproites of Colorado and Wyoming USA. 8th
International Kimberlite Conference Guidebook, Colorado
Wyoming Field Trip, June 16–21. Ottawa: Geological Survey of
Canada.
Dana, E.S., and W.E. Ford. 1951. A Textbook of Mineralogy. 7th
edition. New York: John Wiley & Sons.
Davidson, C.F. 1967. The so-called “cognate xenoliths” of
kimberlites. Pages 251–261 in Ultramafic and Related Rocks.
New York: John Wiley & Sons.
Dempster, A.N., and R. Richard. 1973. Regional geology and
structure. Pages 1–19 in Lesotho Kimberlites. Edited by P.H.
Nixon. Cape Town, South Africa: Cape and Transvaal Printers.
Drew, G.J. 1986. A geophysical case history of the AK1 lamproite.
Pages 454–456 in Proceedings of the 4th International
Kimberlite Conference. Extended Abstracts. Perth: Geological
Survey of Western Australia.
Erlich, E.I., and W.D. Hausel. 2002. Diamond Deposits—Origin,
Exploration, and History of Discoveries. Littleton, CO: SME.
Fipke, C.E., J.J. Gurney, and R.O. Moore. 1995. Diamond
Exploration Techniques Emphasising Indicator Mineral
Geochemistry and Canadian Examples. Bulletin 423. Ottawa:
Geological Survey of Canada.
Gerryts, E. 1967. Diamond prospecting by geophysical methods—a
review of current practice. Pages 439–446 in Mining and
Groundwater Geophysics. Economic Report 26. Ottawa:
Geological Survey of Canada.
Goepel McDermid Securities. 1999. Canadian diamond companies,
new facets in a profitable industry. In Investment Research.
Vancouver: Raymond James.
Gregory, G.P. 1984. Exploration for primary diamond deposits with
special emphasis on the Lennard Shelf, Western Australia.
Pages 475–484 in Proceedings of the Geological Society of
Australia. Edited by P.G. Purcell. Perth: Geological Survey of
Western Australia.
Gregory G.P., and J.S. Tooms. 1969. Geochemical prospecting for
kimberlite. Quarterly of the Colorado School of Mines 64:265–
305.
Haebid, A.E., and D.G. Jackson. 1986. Geochemical expression of
some West Australian kimberlites and lamproites. Pages 466–
468 in Proceedings of the 4th International Kimberlite
Conference. Extended Abstracts. Perth: Geological Survey of
Western Australia.
Harlow, G.E. 1998. The Nature of Diamonds. London: Cambridge
University Press.
Hausel, W.D. 1996. Pacific Coast diamonds—an unconventional
source terrane. Pages 925–934 in Geology and Ore Deposits of
the American Cordillera. Symposium proceedings. Edited by
A.R. Coyner and P.L. Fahey. Reno: Geological Society of
Nevada.
———. 1998. Diamonds and Mantle Source Rocks in the Wyoming
Craton, with a Discussion of other U.S. Occurrences. Report of
Investigations 53. Laramie: Wyoming State Geological Survey.
Hausel, W.D., P.R. Glahn, and T.L. Woodzick. 1981. Geological
and Geophysical Investigations of Kimberlite in the Laramie
Range of Southeastern Wyoming. Preliminary Report 18.
Laramie: Geological Survey of Wyoming.
Diamonds
Hausel, W.D., R.W. Gregory, R.H. Motten, and W.M. Sutherland.
2000. Economic geology of the Iron Mountain kimberlite
district, Wyoming. Pages 151–164 in Classical Wyoming
Geology in the New Millennium. Field Conference Guidebook.
Edited by A.K. Finley and G.A. Winter. Casper: Wyoming
Geological Association.
———. 2003. Geology of the Iron Mountain kimberlite district
(with a summary of investigations of nearby kimberlitic
indicator mineral anomalies in southeastern Wyoming). Report
of Investigations 54. Laramie: Wyoming State Geological
Survey.
Hausel, W.D., R.W. Gregory, and W.M. Sutherland. 1995.
Lamproites, diamond indicator minerals, and related anomalies
in the Green River Basin, Wyoming. Pages 137–151 in
Resources of Southwestern Wyoming. Field Conference
Guidebook. Edited by R.W. Jones. Casper: Wyoming
Geological Association.
Hausel, W.D., M.E. McCallum, and T.L. Woodzick. 1979.
Exploration for Diamond-Bearing Kimberlite in Colorado and
Wyoming: An Evaluation of Exploration Techniques. Report of
Investigations 19. Laramie: Wyoming State Geological Survey.
Helmstaedt, H., and J.J. Gurney. 1995. Geotectonic controls of
primary diamond deposits: Implications for area selection.
Journal of Geochemical Exploration 53:125–144.
Hughes, C.J. 1982. Igneous Petrology. New York: Elsevier.
Hurlbut, C.S., Jr., and G.S. Switzer. 1979. Gemology. New York:
John Wiley & Sons.
Janke, G. 1983. The role of geophysics in the discovery of the
Ellendale and Fitzroy kimberlites. Pages 66–72 in Proceedings
of the 3rd Biennial Conference Australian Society of
Exploration Geophysicists. Brisbane, Australia: Australian
Society of Exploration Geophysicists.
Janse, A.J.A. 1984. Kimberlites—where and when? Pages 19–61 in
Kimberlite Occurrence and Origin: A Basis For Conceptual
Models In Exploration. Publication 8. Edited by J.E. Glover and
P.G. Harris. Perth: University of Western Australia.
———. 1994. Is Clifford’s rule still valid? Affirmative examples
from around the world. Pages 215–235 in Diamonds:
Characterization, Genesis and Exploration. Volume 2. Edited
by H.O.A. Meyer and O.H. Leonardos. Proceedings of the 5th
International Kimberlite Conference. Rio de Janeiro:
Companhia de Pesquisa Recursos Minerais.
———. 1995. A history of diamond sources in Africa: Part I. Gems
& Gemology 31(4):228–255.
———. 1996. A history of diamond sources in Africa: Part II.
Gems & Gemology 32(1):2–30.
Jaques, A.L. 1998. Kimberlite and lamproite diamond pipes.
Australian Geological Survey Journal of Geology and
Geophysics 17(4):153–162.
Jaques, A.L., G.P. Gregory, J.D. Lewis, and J. Ferguson. 1982. The
ultra-potassic rocks of the West Kimberley region, Western
Australia, and a new class of diamondiferous kimberlites. Terra
Cognita 2:251–252.
Jaques, A.L, G.P. Gregory, J.D. Lewis, J. Ferguson, J. Smith, B.W.
Chappell, and M.T. McCulloch. 1983. The ultrapotassic
diamond-bearing rocks of the Western Kimberley region,
Western Australia. Pages 286–287 in Proceedings of the 6th
Geological Society of Australia Convention. Volume 9. Perth:
Geological Survey of Western Australia.
Jaques, A.L., J.D. Lewis, and C.B. Smith. 1986. The Kimberlites
and Lamproites of Western Australia. Bulletin 132. Perth:
Geological Survey of Western Australia.
17
Kaminsky, F.V., S.M. Sablukov, and L.I. Sablukova. 2003.
Diamondiferous Archean lamprophyres with komatiitic
affinities from the Wawa Area, Ontario, Canada. In Proceedings
of the 8th International Kimberlite Conference. Program with
Abstracts. Vancouver: Lithos.
Kennedy, G.C., and B.E. Nordlie. 1968. The genesis of diamond
deposits. Economic Geology 63:495–503.
Kingston, M.J. 1984. Spectral reflectance features of kimberlites
and carbonatites: Implications for remote sensing for
exploration. Pages 1135–1145 in Kimberlites and Related
Rocks. Special Publication 14. Sydney: Geological Society of
Australia.
Kjarsgaard, B.A., and A.A. Levinson. 2002. Diamonds in Canada.
Gems and Gemology 38(3):208–238.
Krajick, K. 2001. Barren Lands. New York: Henry Holt.
Lampietti, E.M.J., and D. Sutherland. 1978. Prospecting for
diamonds—some current aspects. Mining Magazine (August):
117–123.
Levinson, A.A., J.J. Gurney, and M.B. Kirkley. 1992. Diamond
sources and production, past, present and future. Gems and
Gemology 28(4):234–254.
Litinskii, V.A. 1963a. Applications of metallometry and
kappametry in prospecting for kimberlite bodies. International
Geology Review 6(11):2027–2035.
———. 1963b. Measurement of magnetic susceptibility in
prospecting for kimberlite pipes. Mining Magazine 109:137–146.
Lonsdale, K. 1971. Formation of lonsdaleite from single-crystal
graphite. American Mineralogist 56:333–336.
Macnae, C.J. 1979. Kimberlite and exploration geophysics.
Geophysics 44:1395–1416.
———. 1995. Applications of geophysics for the detection of
kimberlites and lamproites. Journal of Geochemical
Exploration 53:213–243.
Mannard, G.W. 1968. The surface expression of kimberlite pipes.
Geological Association of Canada Proceedings 19:15–21.
Mathur, S.M. 1982. The diamond deposits of India. Industrial
Diamond Quarterly 33(3):21–29.
McGretchin, T.R. 1968. The Moses Rock dike: Geology, petrology,
and mode of emplacement of kimberlite-bearing breccia dike,
San Juan County, Utah. Ph.D. dissertation, Pasadena: California
Institute of Technology.
Meyer, H.O.A., B.L. Garwood, D.P. Svisero, and C.B. Smith. 1994.
Alkaline ultrabasic intrusions in western Minas Gerais, Brazil.
Pages 140–155 in Proceedings of the 5th International
Kimberlite Conference. Volume 1. Rio de Janeiro: Companhia
de Pesquisa de Recursos Minerais.
Middlemost, E.A.K., and D.K. Paul. 1984. Indian kimberlites and
the genesis of kimberlite. Chemical Geology 47:249–260.
Milashev, V.A. 1989. Almaz. Legendi i deistvitel’nost’. 3rd edition.
Leningrad: Nedra. (In Russian)
Miller, P. 1995. Diamonds—Commencing the Countdown to
Market Renaissance. London: Yorkton Natural Resources.
Mitchell, R.H., and S.C. Bergman. 1991. Petrology of Lamproites.
New York: Plenum Press.
Nixon, P.H. 1981. Regional diamond exploration—theory and
practice. Pages 64–80 in Kimberlites and Diamonds.
Publication 5. Edited by J.D. Glover and D.I. Groves. Perth:
University of Western Australia Extension Service.
———. 1995. The morphology and nature of primary
diamondiferous occurrences. Journal of Geochemical
Exploration 53:41–71.
18
Industrial Minerals and Rocks
O’Hara, M.J., S.W. Richardson, and G. Wilson. 1971. Garnetperidotite stability and occurrence in crust and mantle.
Contributions to Mineralogy and Petrology 32:48–68.
Olson, D.W. 2001. Diamond (industrial). Pages 23.1–23.4 in
Minerals Yearbook. Reston, VA: U.S. Geological Survey.
———. 2003. Diamond (industrial). Pages 58–59 in Mineral
Commodity Summaries. Reston, VA: U.S. Geological Survey.
Orlov, Y.L. 1977. The Mineralogy of Diamond. New York: John
Wiley & Sons.
Paterson, N.R., and D.A. MacFadyen. 1984. An Airborne EM
(INPUT)/Magnetometer Survey, State Line District, ColoradoWyoming. SME Preprint No. 84-310. Littleton, CO: SME.
Pokhilenko, N.P., D.A. Zedgenizov, N.P. Afanasiev, G.M. Rylov,
H.J. Milledge, A. Jones, A.E. Hall, and L.F. Reimers. 2003.
Morphology and internal structure of diamonds from the Snap
Lake/King Lake kimberlite dyke system, Slave Craton, Canada.
Pages 90–91 in Proceedings of the 8th International Kimberlite
Conference. Program with Abstracts. Vancouver: Lithos.
Robertson, R. 2004. BHP Billiton approves Panda underground
mine at Ekati. The Northern Miner 90(13):1–2.
Rock, N.M.S., B.J., Griffin, A.D. Edgar, D.K. Paul, and J.M. Hergt.
1992. A spectrum of potentially diamondiferous lamproites and
minettes from the Jharia coalfield, eastern India. Journal of
Volcanology and Geothermal Research 50:55–83.
Sakuntala, S., and N.K. Brahman. 1984. Diamond mines near
Raichur. Journal of the Geological Society of India 25(2):780–
786.
Scott-Smith, B.H. 1989. Lamproites. Pages 229–270 in
Undersaturated Alkaline Rocks: Mineralogy, Petrology and
Economic Potential. Edited by R.H. Mitchell. Ottawa:
Mineralogical Association of Canada.
———. 1996. Lamproites. Pages 259–270 in Undersaturated
Alkaline Rocks: Mineralogy, Petrology, and Economic Potential.
Edited by R.H. Mitchell. Ottawa: Mineralogical Association of
Canada.
Shigley, J.E., J. Chapman, and R.K. Ellison. 2001. Discovery and
mining of the Argyle diamond deposit. Australia. Gems and
Gemology 37(1):26–41.
Shigley, J.E., T.E. Moses, I. Reinitz, S. Elen, S.F. McClure, and E.
Fritzch. 1997. Gemological properties of near-colorless
synthetic diamonds. Gems and Gemology 33(1):42–53.
Skinner, E.M.W., C.B. Smith, J.D. Bristow, B.H. Scott-Smith, and
J.B. Dawson. 1985. Proterozoic kimberlites and lamproites and
a preliminary age for the Argyle lamproite pipe, Western
Australia. Transactions, Geological Society of South Africa
22(II):335–340.
Smyshliaev, A. 1999. Geologi Kamchatki. Zoloto, Platina, Almazi.
Petropavlovsk-Kamchatsky, Russia: Kamchatskprirodresurs. (In
Russian).
Sunagawa, I. 1990. A report on a recent visit to the diamond
deposits in Liaoning Province, People’s Republic of China.
Journal of the Gemological Society of Japan 15(1–4):37–45.
Wagner, P.A. 1914. The Diamond Fields of South Africa. 3rd
edition. Johannesburg: Transvaal Leader.
Ward, F. 1979. The incredible crystal diamonds. National
Geographic (January): 85–113.
Watson, K.D. 1967. Kimberlites of eastern North America. In
Ultramafic and Related Rocks. New York: John Wiley & Sons.
Woodzick, T.L. 1980. Potential application of reflectance, soil
temperature and soil moisture data to kimberlite exploration
programs. Geological Society of America Abstracts with
Program 8(6):403.